Measurement Glossary
Explore our comprehensive A-Z glossary of measurement terms, unit definitions, and conversion concepts. From SI units to cooking measurements, find clear explanations with practical examples.
A
Absolute Pressure
Pressure measured relative to a perfect vacuum (zero pressure). Equals gauge pressure plus atmospheric pressure.
If gauge pressure is 32 PSI and atmospheric is 14.7 PSI, absolute pressure is 46.7 PSIA.
Absolute Zero
The lowest possible temperature, 0 Kelvin or -273.15°C (-459.67°F). At this temperature, all molecular motion theoretically stops.
Outer space is about 2.7 K above absolute zero due to cosmic background radiation.
Acceleration
The rate of change of velocity over time. The SI unit is meters per second squared (m/s²).
Earth's gravitational acceleration is about 9.8 m/s².
Accuracy
How close a measured value is to the true or accepted value. A measurement can be precise (consistent) but not accurate (correct).
A scale that consistently shows 5.1 kg for a 5.0 kg weight is precise but not accurate.
Acre
An imperial unit of area equal to 43,560 square feet or about 4,047 square meters. Commonly used for land measurement.
A football field (including end zones) is about 1.32 acres.
Actual Size
The true measured dimensions of a product, as opposed to its nominal (named) size.
A 2×4's actual size is 1.5 × 3.5 inches after drying and planing.
Altitude and Boiling
At high elevations, lower air pressure causes water to boil at lower temperatures, affecting cooking times and baking chemistry.
Pasta takes longer to cook in the mountains because the boiling water is cooler.
Altitude and Pressure
The relationship between elevation and atmospheric pressure. Pressure decreases approximately 1 inHg per 1,000 feet of altitude gain.
At 5,000 feet elevation, atmospheric pressure is about 24.9 inHg vs 29.92 at sea level.
Ampere
The SI base unit of electric current, defined by the flow of electric charge. Commonly called an "amp."
A typical smartphone charger supplies 1-2 amperes of current.
Angle of Incline
The angle between an inclined surface and the horizontal, measured in degrees. Related to slope by: angle = arctan(rise/run).
A wheelchair ramp should have an angle of incline no greater than about 4.8° (1:12 slope).
Angular Velocity
The rate of rotation measured in radians per second (rad/s). Related to RPM by the formula: rad/s = RPM × 2π/60.
A wheel spinning at 60 RPM has an angular velocity of about 6.28 rad/s.
Approximation
An inexact value that is close enough to the true value for practical purposes. Quick mental conversions often use approximations.
Approximating 1 mile ≈ 1.6 km (exact: 1.609344 km) for quick mental math.
Are
A metric unit of area equal to 100 square meters. Rarely used alone but forms the basis for hectare (100 ares).
1 hectare = 100 ares = 10,000 square meters.
Astronomical Unit
The average distance from Earth to the Sun, about 149.6 million kilometers (93 million miles). Used for measuring distances within the solar system.
Mars is about 1.5 AU from the Sun.
Atmosphere
A unit of pressure defined as 101,325 Pascals, representing average sea-level atmospheric pressure.
Scuba divers experience 2 atmospheres of pressure at 10 meters depth.
AWG
American Wire Gauge, a standard system for measuring wire diameter. Used for electrical wiring.
14 AWG wire is standard for 15-amp circuits; 12 AWG for 20-amp circuits.
B
Baker's Percentage
A system where all ingredient weights are expressed as percentages of the flour weight. Flour is always 100%.
A bread recipe at 65% hydration uses 650g water for every 1000g flour.
Baking Temperature
The oven heat level for baking. Low (250-325°F/120-165°C) for slow cooking; moderate (350°F/180°C) for cakes; high (400°F+/200°C+) for bread.
Most cookies bake at 350°F (180°C); pizza needs 450-500°F (230-260°C).
Bandwidth
The maximum rate of data transfer across a network path. Often confused with speed; bandwidth is capacity, not actual throughput.
A 1 Gbps fiber connection has more bandwidth than a 100 Mbps cable connection.
Bar
A metric unit of pressure equal to 100,000 Pascals, approximately equal to atmospheric pressure at sea level.
Tire pressure in Europe is often measured in bar (e.g., 2.2 bar).
Barometric Pressure
The pressure exerted by the atmosphere at a given point. Decreases with altitude and changes with weather systems.
Falling barometric pressure often indicates approaching storms.
Barrel
A unit of volume that varies by commodity. An oil barrel is 42 US gallons (159 liters); a beer barrel is 31 US gallons.
Oil prices are quoted per barrel (42 gallons or 159 liters).
Base Unit
A fundamental unit in a measurement system that is defined independently, not derived from other units. The SI system has seven base units from which all other units are derived.
The meter is a base unit for length; the square meter (area) is a derived unit.
Bit
The smallest unit of digital data, representing a single binary digit (0 or 1). Eight bits make one byte.
Internet speed is measured in bits per second (Mbps = megabits per second).
Board Foot
A unit of lumber volume equal to 144 cubic inches (a board 1 foot × 1 foot × 1 inch). Used for pricing hardwood.
A 2×4×8 board contains about 5.3 board feet.
Boiling Point
The temperature at which a liquid turns to gas at a given pressure. Water boils at 100°C (212°F) at sea level.
At high altitude, water boils at lower temperatures due to reduced air pressure.
Boiling Point of Water
The temperature at which water turns to steam: 100°C (212°F) at sea level. Decreases at higher altitudes due to lower air pressure.
In Denver (5,280 ft), water boils at about 95°C (203°F).
BTU
British Thermal Unit, the energy needed to raise 1 pound of water by 1°F. Used for heating/cooling capacity in the US.
Air conditioners are rated by BTU/hour; a window unit might be 8,000 BTU.
Byte
The basic unit of digital storage, consisting of 8 bits. Can represent 256 different values (0-255).
A single text character typically uses 1 byte of storage.
C
Calibration
The process of adjusting an instrument so its readings match known standard values. Essential for maintaining measurement accuracy.
Calibrating a kitchen scale with a known 500g weight to ensure accurate measurements.
Calorie
A unit of energy. The small calorie (cal) is the energy to raise 1g of water by 1°C. The food Calorie (kcal) equals 1,000 small calories.
A medium apple contains about 95 food Calories (kcal).
Candela
The SI base unit of luminous intensity—the power emitted by a light source in a particular direction, weighted by human eye sensitivity.
A typical candle emits about 1 candela of light.
Carat
A unit of mass for gemstones equal to 200 milligrams (0.2 grams). Not to be confused with karat (gold purity).
A 1-carat diamond weighs 0.2 grams or 200 milligrams.
Celsius
A temperature scale where 0° is the freezing point of water and 100° is the boiling point at standard pressure. Used by most countries worldwide.
Normal human body temperature is about 37°C.
Centi
A metric prefix meaning one hundredth (10⁻² or 0.01). Most commonly used with meters.
1 centimeter = 0.01 meters; there are 100 centimeters in a meter.
Centimeter
A metric unit of length equal to one hundredth of a meter (0.01 m) or about 0.394 inches. Commonly used for body measurements and small objects.
A standard credit card is about 8.5 cm wide.
Conversion Factor
A numerical ratio used to convert a measurement from one unit to another. It equals 1 when the numerator and denominator represent the same quantity in different units.
The conversion factor from inches to centimeters is 2.54 (1 inch = 2.54 cm).
Cooking Yield
The amount of food remaining after cooking, typically less than raw weight due to moisture loss. Important for recipe planning.
Raw meat shrinks about 25% when cooked—1 lb raw beef yields about 12 oz cooked.
Cubic Foot
An imperial unit of volume equal to a cube with 1-foot sides, about 28.3 liters. Used for shipping and construction.
Refrigerator capacity is often measured in cubic feet.
Cubic Meter
The SI derived unit of volume, equal to the volume of a cube with 1-meter sides. Equals 1,000 liters.
Natural gas is often billed in cubic meters.
Cubic Yard
A unit of volume equal to 27 cubic feet (3 ft × 3 ft × 3 ft). Used for concrete, soil, and bulk materials.
A typical concrete truck holds 8-10 cubic yards of concrete.
Cup
A cooking volume measure equal to 8 fluid ounces (US) or about 237 ml. Metric cups are 250 ml.
A recipe calling for 2 cups of flour means about 474 ml in US measurements.
D
Dash
A small amount in cooking, typically about 1/8 teaspoon. Slightly more than a pinch.
A dash of hot sauce adds flavor without overwhelming heat.
Deca
A metric prefix meaning ten (10¹). Rarely used in everyday measurements.
1 decameter = 10 meters.
Deci
A metric prefix meaning one tenth (10⁻¹ or 0.1). Less commonly used than other prefixes.
1 decimeter = 0.1 meters = 10 centimeters.
Derived Unit
A unit of measurement that is defined by combining base units through multiplication or division. Examples include velocity (m/s), force (Newton = kg·m/s²), and energy (Joule = kg·m²/s²).
The Newton, a unit of force, is derived from kg × m/s².
Dew Point
The temperature at which air becomes saturated with water vapor and dew forms. Higher dew points indicate more humid conditions.
A dew point above 65°F (18°C) feels uncomfortable; above 75°F (24°C) feels oppressive.
Differential Pressure
The difference in pressure between two points. Used to measure flow rates, filter conditions, and level differences in tanks.
An air filter is replaced when the differential pressure across it exceeds a threshold.
Dimensional Analysis
A mathematical technique for converting units by treating units as algebraic quantities that can be multiplied, divided, and canceled. Also called factor-label method or unit analysis.
Converting 60 mph to m/s: 60 mi/hr × (1609 m/1 mi) × (1 hr/3600 s) = 26.8 m/s.
E
Efficiency
The ratio of useful output to total input, usually expressed as a percentage. No machine is 100% efficient due to energy losses.
A LED bulb is about 80% efficient; an incandescent bulb is only about 5% efficient at producing light.
Electrical Power
Power in electrical circuits, calculated as voltage × current (P = V × I). Measured in watts. Also related to resistance: P = I²R.
A 120V outlet supplying 10 amps delivers 1,200 watts of electrical power.
Electron Volt
A unit of energy used in physics, equal to the energy gained by an electron accelerated through 1 volt (about 1.6 × 10⁻¹⁹ joules).
Particle physics experiments measure energies in GeV (billions of electron volts).
Energy
The capacity to do work or transfer heat. Can exist in various forms: kinetic, potential, thermal, electrical, chemical, nuclear.
A moving car has kinetic energy; a battery stores chemical energy.
Energy vs Power
Energy is the total capacity to do work (measured in joules); power is the rate of energy use (joules per second = watts). A 100W bulb uses energy faster than a 60W bulb.
A 1000W microwave running for 2 minutes uses 33 Wh of energy (1000W × 2/60 hours).
Error
The difference between a measured value and the true value. Can be systematic (consistent bias) or random (unpredictable variation).
If a ruler consistently measures 1 mm short, all measurements have a -1 mm systematic error.
Estimation
Making an educated guess about a measurement or conversion result without precise calculation. Useful for quick sanity checks.
Estimating that 100 kg is roughly 220 lbs (exact: 220.46 lbs).
Exponent
A number indicating how many times a base number is multiplied by itself. In metric prefixes, exponents define the relationship to the base unit.
10³ = 1,000 (10 multiplied by itself 3 times).
F
Fahrenheit
A temperature scale where 32° is the freezing point of water and 212° is the boiling point. Primarily used in the United States.
Normal human body temperature is about 98.6°F.
Fathom
A nautical unit of length equal to 6 feet (1.829 meters). Traditionally used to measure water depth.
The phrase "deep six" comes from burying something at least six fathoms (36 feet) underwater.
Flour and Sugar Conversion
Converting between volume and weight for common baking ingredients. 1 cup all-purpose flour ≈ 120-130g; 1 cup granulated sugar ≈ 200g.
To substitute: 2 cups flour (240g) plus 1 cup sugar (200g) = 440g total dry ingredients.
Fluid Measure
Volume measurements for liquids, as opposed to dry measures. Liquid and dry measuring cups may give different results.
Use a liquid measuring cup (with a spout) for milk, and a dry cup for flour.
Fluid Ounce
A unit of volume: US fluid ounce is about 29.57 ml; Imperial fluid ounce is about 28.41 ml. Different from weight ounces.
A can of soda typically contains 12 fluid ounces (355 ml).
Foot
An imperial/US customary unit of length equal to 12 inches or about 30.48 centimeters. Originally based on the length of a human foot.
A basketball hoop is 10 feet high.
Foot-Pound (Torque)
An imperial unit of torque equal to one pound-force applied at a one-foot lever arm. Common in US automotive and construction.
Engine torque specs often say "tighten to 25 ft·lb."
Force vs Torque
Force causes linear motion (measured in Newtons); torque causes rotational motion (measured in Newton-meters). Torque = force × lever arm distance.
Pushing a door near the hinges requires more force than pushing near the handle to produce the same torque.
Freezing Point
The temperature at which a liquid turns to solid at a given pressure. Pure water freezes at 0°C (32°F) at sea level.
Salt lowers the freezing point of water, which is why we use it on icy roads.
Frequency
The number of occurrences of a repeating event per unit time. Measured in Hertz (cycles per second).
FM radio stations broadcast at frequencies around 100 MHz.
G
G-Force
A measure of acceleration relative to Earth's gravity (g = 9.8 m/s²). 1g is normal gravity; 2g is twice that force.
Roller coaster riders may experience 3-4 g during sharp turns.
Gallon
A unit of volume with two definitions: US gallon (3.785 liters) and Imperial gallon (4.546 liters). Used for fuel and large liquid quantities.
A US gallon of milk contains about 3.785 liters.
Gauge
A measurement system for wire and sheet metal thickness. Counterintuitively, higher gauge numbers mean thinner material.
12-gauge wire is thicker than 14-gauge wire.
Gauge Pressure
Pressure measured relative to atmospheric pressure. A gauge reading of 0 means the pressure equals atmospheric pressure, not a true vacuum.
A tire gauge reading 32 PSI means the tire pressure is 32 PSI above atmospheric pressure.
Giga
A metric prefix meaning one billion (10⁹ or 1,000,000,000). Frequently used for data storage and processing speeds.
1 gigabyte = 1,000 megabytes; a 5G network operates at gigahertz frequencies.
Gigabyte
A unit of digital storage equal to 1,000 megabytes or 1 billion bytes. Common for storage devices and mobile data plans.
A typical smartphone has 64-256 gigabytes of storage.
GMT
Greenwich Mean Time, the mean solar time at the Royal Observatory in Greenwich, London. Often used interchangeably with UTC.
London is on GMT in winter and GMT+1 in summer.
Grade (Percent)
Slope expressed as a percentage: (rise ÷ run) × 100. A 100% grade means the rise equals the run (45° angle).
A road with a 6% grade rises 6 feet for every 100 feet of horizontal distance.
Gram
A metric unit of mass equal to one thousandth of a kilogram. Originally defined as the mass of 1 cubic centimeter of water.
A US dollar bill weighs about 1 gram.
H
Heaping
A measurement where ingredients are piled above the rim of the measuring cup or spoon.
A heaping tablespoon of sugar is more than a level tablespoon.
Heat Index
A measure of how hot it feels when humidity is factored in with air temperature. Also called apparent temperature.
A temperature of 90°F with 65% humidity has a heat index of about 103°F.
Hectare
A metric unit of area equal to 10,000 square meters or about 2.471 acres. Used internationally for land measurement.
A soccer field is about 0.7 hectares.
Hecto
A metric prefix meaning one hundred (10²). Most commonly seen in hectopascals (weather) and hectares (area).
Weather pressure is often reported in hectopascals (hPa); 1 hectare = 100 ares.
Hertz
The SI unit of frequency, equal to one cycle per second. Used for sound waves, electromagnetic radiation, and clock speeds.
Middle C on a piano is about 262 Hz; a computer processor might run at 3 GHz.
Horsepower
A unit of power originally defined by James Watt. Mechanical horsepower equals about 746 watts.
A typical car engine produces 150-300 horsepower.
I
Imperial System
A system of measurement originating in Britain, using units like inches, feet, pounds, and gallons. It remains in common use in the United States, Liberia, and Myanmar, and partially in the UK.
A recipe might call for 2 cups of flour, measured using the US customary system derived from imperial units.
Inch
An imperial/US customary unit of length equal to 1/12 of a foot or exactly 2.54 centimeters. Commonly used for screen sizes, paper dimensions, and small measurements.
A smartphone screen might be 6.5 inches diagonally.
Inches of Mercury
A unit of pressure based on the height of a mercury column. Used in US weather reports and aviation for barometric pressure.
Standard sea-level pressure is 29.92 inches of mercury (inHg).
Ingredient Density
The mass per volume of an ingredient. Dense ingredients (honey) weigh more per cup than light ones (flour). Critical for volume-to-weight conversions.
1 cup of honey weighs 340g, while 1 cup of flour weighs only 120-130g.
J
Joule
The SI unit of energy, equal to the work done by a force of one Newton moving an object one meter. Also used for heat and electrical energy.
Lifting a 1 kg object 1 meter requires about 9.8 joules of energy.
Joule vs Calorie
Both measure energy. The joule is the SI unit; the calorie is traditional for food and heat. 1 food Calorie (kcal) = 4,184 joules.
A banana has about 105 food Calories or 439,000 joules of energy.
K
Kelvin
The SI base unit of temperature, using the same increment size as Celsius but starting at absolute zero (-273.15°C). Used in science and engineering.
Water freezes at 273.15 K and boils at 373.15 K.
Kilo
A metric prefix meaning one thousand (10³ or 1,000). Used with many units to indicate larger quantities.
1 kilogram = 1,000 grams; 1 kilometer = 1,000 meters.
Kilobyte
A unit of digital storage equal to 1,000 bytes (decimal) or 1,024 bytes (binary). The binary version is now called kibibyte.
A plain text email might be 5-10 kilobytes.
Kilogram
The SI base unit of mass, now defined in terms of the Planck constant. Equals 1,000 grams or approximately 2.205 pounds.
1 liter of water weighs exactly 1 kilogram at 4°C.
Kilometer
A metric unit of length equal to 1,000 meters (about 0.621 miles). Commonly used for road distances and geographic measurements.
A 5K race covers 5 kilometers, or about 3.1 miles.
Kilopascal
A metric unit of pressure equal to 1,000 Pascals. Commonly used for tire pressure in countries using metric.
Tire pressure of 35 PSI equals about 241 kPa.
Kilowatt
A unit of power equal to 1,000 watts. Commonly used for electrical equipment and household power consumption.
A microwave might use 1.2 kilowatts when running.
Kilowatt-Hour
A unit of energy equal to using 1,000 watts for one hour (3.6 million joules). The standard billing unit for electricity.
Running a 100W bulb for 10 hours uses 1 kilowatt-hour of energy.
Kitchen Scale
A device for weighing ingredients, typically measuring in grams and ounces. Essential for accurate baking and recipe scaling.
A digital kitchen scale accurate to 1 gram is ideal for most baking.
Knot
A unit of speed equal to one nautical mile per hour, about 1.151 mph or 1.852 km/h. Used in maritime and aviation.
A commercial airplane cruises at about 450-500 knots.
L
Latency
The delay between sending a request and receiving a response, usually measured in milliseconds. Critical for real-time applications.
Gaming requires low latency (under 50 ms); video calls work well under 150 ms.
League
A historical unit of distance that varied by region, typically about 3 miles (4.8 km). Now obsolete but appears in literature.
"Twenty Thousand Leagues Under the Sea" refers to horizontal distance traveled, not depth.
Level Measure
A measurement where ingredients are leveled off flat with the rim, using a straight edge. The standard for most recipes.
Level off flour by scraping a knife across the measuring cup rim.
Light-Year
The distance light travels in one year in a vacuum, approximately 9.461 trillion kilometers (5.879 trillion miles). Used for astronomical distances.
The nearest star to our Sun, Proxima Centauri, is about 4.24 light-years away.
Linear Conversion
A conversion where the output is directly proportional to the input (y = mx). Most unit conversions are linear.
Inches to centimeters is linear: cm = inches × 2.54.
Linear Foot
A measurement of length only (1 foot = 12 inches), regardless of width or height. Used for molding, countertops, and fencing.
Kitchen countertops are often priced per linear foot.
Liter
A metric unit of volume equal to 1,000 cubic centimeters or about 0.264 US gallons. Originally defined as the volume of 1 kg of water.
A standard water bottle often holds 1 liter.
Long Ton
The Imperial ton, equal to 2,240 pounds or about 1,016 kilograms. Used in the UK for certain goods like coal.
Ship displacement was traditionally measured in long tons.
Lumen
A unit of luminous flux—the total amount of visible light emitted by a source. Used to rate light bulbs.
A 60-watt incandescent bulb produces about 800 lumens.
Lux
A unit of illuminance—the amount of light falling on a surface (lumens per square meter).
An office should have about 500 lux; direct sunlight can exceed 100,000 lux.
M
Mach Number
The ratio of an object's speed to the speed of sound. Mach 1 is the speed of sound, Mach 2 is twice the speed of sound.
The Concorde cruised at Mach 2, or about 1,350 mph.
Map Scale
The ratio between a distance on a map and the corresponding real-world distance. Expressed as a ratio (1:24,000) or representative fraction.
On a 1:24,000 map, 1 inch represents 24,000 inches (2,000 feet) in reality.
Mass
The amount of matter in an object, measured in kilograms. Unlike weight, mass remains constant regardless of gravity.
An astronaut has the same mass on Earth and the Moon, but weighs less on the Moon due to lower gravity.
Material Thickness
The measurement of how thick a material is, often specified in gauge (for metal/wire) or in fractions of an inch or millimeters.
18-gauge sheet metal is about 1.2mm thick; 10-gauge is about 3.4mm thick.
Mechanical Advantage
The factor by which a machine multiplies force or motion. Levers, pulleys, and gears provide mechanical advantage.
A 3:1 pulley system provides a mechanical advantage of 3, reducing the force needed by one-third.
Mega
A metric prefix meaning one million (10⁶ or 1,000,000). Commonly used in computing and engineering.
1 megabyte = 1,000,000 bytes (or 1,048,576 bytes in binary).
Megabit
A unit of data transfer equal to 1,000,000 bits (not bytes). Internet speeds are typically measured in Mbps.
A 100 Mbps internet connection can download about 12.5 megabytes per second.
Megabyte
A unit of digital storage equal to 1,000 kilobytes or 1,000,000 bytes. Photos typically range from 2-5 MB.
A 3-minute MP3 song is about 3-4 megabytes.
Megapascal
A metric unit of pressure equal to 1,000,000 Pascals (1,000 kPa). Used for high-pressure applications like hydraulics and material strength.
Concrete compressive strength is typically 20-40 MPa.
Meter
The SI base unit of length, originally defined as one ten-millionth of the distance from the equator to the North Pole. Now defined by the speed of light: the distance light travels in 1/299,792,458 of a second.
A typical door is about 2 meters tall.
Metric System
A decimal-based system of measurement that uses powers of ten for unit conversions. Developed during the French Revolution, it forms the foundation of the modern SI system and is used by most countries worldwide.
1 kilometer = 1,000 meters = 100,000 centimeters, all related by powers of 10.
Metric Ton
A unit of mass equal to 1,000 kilograms or approximately 2,205 pounds. Also called a tonne.
An average car weighs about 1.5 metric tons.
Micro
A metric prefix meaning one millionth (10⁻⁶ or 0.000001). Used for very small measurements, represented by the Greek letter μ (mu).
Bacteria are measured in micrometers (μm); 1 microgram = 0.000001 grams.
Micron
Informal term for micrometer (μm), one millionth of a meter. Used in manufacturing, biology, and air filtration.
Human hair is typically 70-100 microns in diameter.
Mile
An imperial/US customary unit of length equal to 5,280 feet or 1,760 yards (approximately 1.609 kilometers). Commonly used for road distances in the US and UK.
The distance from New York to Boston is about 215 miles.
Milli
A metric prefix meaning one thousandth (10⁻³ or 0.001). Used for small measurements.
1 millimeter = 0.001 meters; 1 milliliter = 0.001 liters.
Milliamp-Hour
A unit of electrical charge capacity equal to 1/1000 of an amp-hour. Common for rating small battery capacity.
A smartphone battery might be rated at 4,000 mAh.
Milliliter
A metric unit of volume equal to one thousandth of a liter or 1 cubic centimeter. Commonly used for medicine and cooking.
A teaspoon holds about 5 milliliters.
Millimeter
A metric unit of length equal to one thousandth of a meter (0.001 m) or about 0.039 inches. Used for precise measurements in engineering and science.
Rainfall is typically measured in millimeters; a dime is about 1.35 mm thick.
Millisecond
One thousandth of a second (0.001 s). Used in computing, sports timing, and scientific measurements.
A human eye blink takes about 300-400 milliseconds.
mmHg
Millimeters of mercury, a unit of pressure based on the height of a mercury column. Used for blood pressure and vacuum.
Normal blood pressure is about 120/80 mmHg.
Mole
The SI unit for amount of substance, equal to about 6.022 × 10²³ particles (Avogadro's number).
One mole of water (18 grams) contains 6.022 × 10²³ water molecules.
N
Nano
A metric prefix meaning one billionth (10⁻⁹ or 0.000000001). Used in nanotechnology and atomic-scale measurements.
Computer chips are manufactured with transistors measured in nanometers (nm).
Nautical Mile
A unit of length used in maritime and aviation, equal to exactly 1,852 meters or about 1.151 statute miles. Based on one minute of arc of latitude.
A ship traveling at 20 knots covers 20 nautical miles per hour.
Newton
The SI unit of force, equal to the force needed to accelerate 1 kilogram at 1 meter per second squared (1 N = 1 kg·m/s²).
An apple weighs about 1 Newton on Earth.
Newton-Meter
The SI unit of torque, equal to the force of one Newton applied at a one-meter lever arm. Used in automotive and mechanical specifications.
An electric motor might produce 400 N·m of torque.
Nominal Size
The named size of a product, which may differ from its actual dimensions. Common in lumber and pipes.
A nominal 2×4 board actually measures 1.5 × 3.5 inches.
Non-Linear Conversion
A conversion where the relationship between input and output is not a simple multiplication. Temperature conversions between Fahrenheit and Celsius are non-linear due to offset.
Celsius to Fahrenheit: °F = (°C × 9/5) + 32 includes both multiplication and addition.
O
Ohm
The SI unit of electrical resistance. One ohm allows one ampere of current to flow when one volt is applied.
Headphones typically have an impedance of 16-600 ohms.
Order of Magnitude
The power of 10 closest to a number, used to compare sizes of quantities. Two values differing by one order of magnitude means one is about 10 times the other.
1,000 is two orders of magnitude larger than 10 (10³ vs 10¹).
Ounce
An imperial unit of mass equal to 1/16 of a pound or about 28.35 grams. Used for food portions, mail, and precious metals.
A standard slice of bread weighs about 1 ounce.
Oven Temperature Conversion
Converting between °F, °C, and gas marks for baking. Common temperatures: 350°F = 180°C = Gas 4; 400°F = 200°C = Gas 6.
A recipe at 375°F needs the oven set to 190°C or Gas Mark 5.
P
Packed Cup
A measurement where ingredients (especially brown sugar) are firmly pressed into the cup, eliminating air pockets.
1 packed cup of brown sugar weighs about 220 grams.
Parsec
An astronomical unit of length equal to about 3.26 light-years or 206,265 AU. Defined as the distance at which one AU subtends an angle of one arcsecond.
The Andromeda Galaxy is about 778,000 parsecs from Earth.
Pascal
The SI unit of pressure, equal to one Newton per square meter. Named after Blaise Pascal.
Standard atmospheric pressure is about 101,325 Pascals.
Period
The time taken for one complete cycle of a repeating event. The reciprocal of frequency.
A 60 Hz AC power signal has a period of 1/60 second (about 16.7 milliseconds).
Peta
A metric prefix meaning one quadrillion (10¹⁵ or 1,000,000,000,000,000). Used in scientific computing and data centers.
Supercomputers can process petaflops (quadrillions of floating-point operations per second).
Pico
A metric prefix meaning one trillionth (10⁻¹² or 0.000000000001). Used in electronics and physics.
Capacitors in electronics are often measured in picofarads (pF).
Pinch
An approximate cooking measurement, typically 1/16 teaspoon or the amount you can hold between thumb and forefinger.
Add a pinch of salt to enhance the flavor.
Pint
A unit of volume equal to 1/2 quart. A US pint is about 473 ml; an Imperial pint is about 568 ml.
A pint of beer in the UK is 568 ml, larger than a US pint at 473 ml.
Pixel
The smallest addressable element in a digital image or display. Screen resolution is measured in pixels (e.g., 1920×1080).
A 4K display has about 8.3 million pixels (3840 × 2160).
Pound
An imperial unit of mass equal to 16 ounces or approximately 453.6 grams. The most common unit for body weight in the US.
A gallon of water weighs about 8.34 pounds.
Power
The rate at which energy is transferred or converted. Measured in watts (joules per second).
A more powerful motor can do the same work in less time.
Power-to-Weight Ratio
A measure of performance comparing power output to mass, usually in horsepower per ton or watts per kilogram. Higher values indicate better acceleration.
A sports car with 400 hp and 1,500 kg has a power-to-weight ratio of 267 hp/ton.
Precision
The degree to which repeated measurements show the same result. Also refers to the number of significant digits in a value.
Measuring 2.54, 2.53, and 2.54 cm shows high precision; measuring 2.3, 2.8, and 2.1 cm shows low precision.
Prefix
A modifier placed before a unit name to indicate a multiple or fraction of that unit. Common metric prefixes include kilo- (1,000), centi- (0.01), milli- (0.001), and micro- (0.000001).
Kilo- means 1,000, so 1 kilometer = 1,000 meters.
Pressure vs Force
Force is a push or pull measured in Newtons; pressure is force distributed over an area (force ÷ area). The same force creates more pressure on a smaller area.
High heels exert more pressure on floors than flat shoes because the same body weight acts on a smaller area.
Proportion
An equation stating that two ratios are equal. Used to solve conversion problems by setting up equivalent relationships.
If 1 inch = 2.54 cm, then x inches = 10 cm can be solved: x = 10/2.54 = 3.94 inches.
PSI
Pounds per square inch, an imperial unit of pressure commonly used in the US for tire pressure and hydraulics.
Car tires are typically inflated to 30-35 PSI.
Q
Quart
A unit of volume equal to 1/4 gallon. A US quart is about 0.946 liters; an Imperial quart is about 1.137 liters.
Motor oil is often sold in quart containers.
R
R-Value
A measure of thermal resistance in insulation. Higher R-values indicate better insulating ability.
Attic insulation in cold climates should be R-49 or higher.
Rankine
An absolute temperature scale using Fahrenheit-sized degrees. Zero Rankine is absolute zero (0 K), and 491.67 R equals 32°F.
The Rankine scale is used in some US engineering applications.
Ratio
A comparison of two quantities expressed as a fraction or with a colon. In conversions, ratios show the relationship between different units.
The ratio of feet to meters is approximately 3.281:1.
Repeatability
The ability of an instrument or method to produce the same result when the same quantity is measured multiple times under identical conditions.
A stopwatch with good repeatability will show nearly the same time for repeated measurements of identical events.
Reproducibility
The ability to obtain consistent results when measurements are made by different people, instruments, or in different locations.
A well-defined measurement procedure should give the same result whether performed in New York or Tokyo.
Resolution
The smallest change in a quantity that can be detected by a measuring instrument. Higher resolution allows more precise readings.
A scale with 0.1g resolution can distinguish between 100.0g and 100.1g; one with 1g resolution cannot.
Rise and Run
The vertical distance (rise) and horizontal distance (run) that define a slope. Common in stair construction and roofing.
Building code often requires stairs with 7" rise and 11" run for safe climbing.
Rounding
The process of reducing the number of digits in a value while keeping it close to the original. Standard practice is to round up at 5 or above.
3.14159 rounded to 2 decimal places is 3.14.
RPM
Revolutions per minute, a unit of rotational speed measuring how many complete turns occur in one minute.
A car engine idles at about 800 RPM and redlines around 6,000-7,000 RPM.
S
Scale Factor
The multiplier used to enlarge or reduce dimensions proportionally. Used in models, blueprints, and manufacturing.
A 1:10 scale model uses dimensions 1/10 of the original; a 5 ft door becomes 6 inches.
Scaling
Adjusting all values in a measurement or recipe by the same factor to maintain proportions while changing the total amount.
Scaling a recipe from 4 servings to 8 servings requires multiplying all ingredients by 2.
Scant
A measurement just under the specified amount—not quite full. The opposite of heaping.
A scant cup of flour is slightly less than a full cup.
Scientific Notation
A way of expressing numbers as a decimal between 1 and 10 multiplied by a power of 10. Makes very large or small numbers easier to work with.
The speed of light (299,792,458 m/s) in scientific notation is 2.998 × 10⁸ m/s.
Second
The SI base unit of time, defined by the radiation frequency of cesium-133 atoms (9,192,631,770 cycles per second).
Light travels about 300,000 kilometers in one second.
Sensitivity
How much the output of a measuring instrument changes in response to a change in the quantity being measured.
A highly sensitive scale will show a reading change when a single drop of water is added.
Serving Size
A standardized portion for nutritional comparison. US FDA defines serving sizes; actual consumed portions often differ.
A pasta serving size is typically 2 oz (56g) dry, yielding about 1 cup cooked.
Short Ton
The US customary ton, equal to 2,000 pounds or about 907 kilograms. Commonly used in the US for freight and commodities.
Coal is often sold by the short ton in the United States.
SI Units
The International System of Units (SI) is the modern form of the metric system and the world's most widely used system of measurement. It comprises seven base units: meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity).
When scientists measure mass, they use kilograms (kg) as the SI base unit rather than pounds.
Significant Figures
The digits in a number that carry meaningful information about its precision. In conversions, the result should have no more significant figures than the least precise input value.
2.5 cm × 2.54 = 6.35 cm, but should be reported as 6.4 cm (2 significant figures).
Slope
The steepness of an incline, expressed as rise over run (vertical change ÷ horizontal change). Can be written as a ratio, percentage, or angle.
A roof with 6:12 slope rises 6 inches for every 12 inches of horizontal distance.
Speed
The rate at which an object covers distance, without regard to direction. Measured in units like m/s, km/h, or mph.
The speed of sound is about 343 m/s in air at room temperature.
Speed of Light
The maximum speed at which energy or information can travel: exactly 299,792,458 m/s in a vacuum. Denoted by c.
Light from the Sun takes about 8.3 minutes to reach Earth.
Square Foot
An imperial unit of area equal to a square with 1-foot sides, about 0.093 square meters. Used for real estate in the US.
A 1,500 square foot house is about 139 square meters.
Square Kilometer
A metric unit of area equal to 1,000,000 square meters or 100 hectares. Used for geographic and national area measurements.
Central Park in New York City covers about 3.41 square kilometers.
Square Meter
The SI derived unit of area, equal to a square with 1-meter sides. Used for floor space, land area, and surface measurements.
A typical parking space is about 12 square meters.
Square Mile
An imperial unit of area equal to 640 acres or about 2.59 square kilometers. Used for large land areas in US/UK.
Manhattan has an area of about 23 square miles.
Square Yard
An imperial unit of area equal to 9 square feet or about 0.836 square meters. Used for carpeting and fabric.
Carpet is often priced per square yard.
Standard
A reference object or value used to define or calibrate units of measurement. National standards laboratories maintain primary standards.
The International Prototype Kilogram was the standard for mass until 2019 when it was redefined using Planck's constant.
Standard Atmosphere
A reference pressure defined as exactly 101,325 Pascals (1 atm). Used as a standard for scientific calculations and altitude measurements.
Aircraft altimeters are calibrated to standard atmosphere for consistent altitude readings.
Stick of Butter
A US butter measurement equal to 1/2 cup, 8 tablespoons, or 113 grams. Wrapper markings show tablespoon divisions.
Most cookie recipes call for 1-2 sticks of butter.
Stone
A British unit of mass equal to 14 pounds (about 6.35 kg). Still used in the UK and Ireland for body weight.
A person weighing 140 pounds weighs 10 stone.
Supersonic
Traveling faster than the speed of sound (Mach 1). Creates a sonic boom when the sound barrier is broken.
Fighter jets can fly at supersonic speeds above Mach 1.
T
Tablespoon
A cooking volume measure equal to 3 teaspoons, about 15 ml (US) or 20 ml (Australia). Commonly abbreviated as tbsp or T.
1 tablespoon of butter weighs about 14 grams.
Teaspoon
A cooking volume measure equal to about 5 ml (US) or 1/3 tablespoon. Commonly abbreviated as tsp or t.
Most recipes call for 1 teaspoon of vanilla extract.
Teaspoon vs Tablespoon
A tablespoon equals 3 teaspoons. Teaspoons are about 5 mL; tablespoons are about 15 mL. Confusing them can ruin recipes.
1 tablespoon of baking powder is 3× more than 1 teaspoon—a common recipe mistake.
Tera
A metric prefix meaning one trillion (10¹² or 1,000,000,000,000). Commonly used for large data storage capacities.
A 2 terabyte hard drive can store 2,000 gigabytes of data.
Terabyte
A unit of digital storage equal to 1,000 gigabytes or 1 trillion bytes. Common for hard drives and cloud storage.
A 1 terabyte drive can store about 250,000 photos or 500 hours of HD video.
Thermal Energy
Heat energy that flows between objects at different temperatures. Measured in joules, calories, or BTUs.
Boiling a cup of water requires adding about 100,000 joules of thermal energy.
Thermal Expansion
The tendency of matter to change volume in response to temperature changes. Most materials expand when heated and contract when cooled.
Bridges have expansion joints to accommodate thermal expansion in summer heat.
Thread Pitch
The distance between screw threads, measured in threads per inch (imperial) or millimeters between threads (metric).
An M8×1.25 bolt has 8mm diameter and 1.25mm thread pitch.
Time Zone
A region that observes a uniform standard time. The world is divided into 24 primary time zones, each 15° of longitude wide.
The US spans 6 time zones from Eastern (UTC-5) to Hawaii (UTC-10).
Tolerance
The acceptable range of variation in a measurement or dimension. Used in manufacturing and engineering specifications.
A bolt with diameter 10 mm ± 0.1 mm has a tolerance of 0.2 mm.
Torque
A rotational force that causes an object to rotate around an axis. Measured in Newton-meters (N·m) or foot-pounds (ft·lb). Used for engines, bolts, and tools.
A car engine might produce 350 N·m of torque; lug nuts should be tightened to about 100 ft·lb.
Torr
A unit of pressure equal to 1/760 of an atmosphere, or about 133.3 Pascals. Named after Evangelista Torricelli.
Vacuum levels are often measured in Torr; 1 Torr ≈ 1 mmHg.
Traceability
The ability to relate measurement results to national or international standards through an unbroken chain of comparisons.
A calibrated thermometer is traceable to NIST (National Institute of Standards and Technology) standards.
Troy Ounce
A unit of mass used for precious metals, equal to about 31.1 grams (heavier than a regular ounce at 28.35 grams).
Gold prices are quoted per troy ounce, not per regular ounce.
U
U-Value
A measure of heat transfer through a material (thermal transmittance). Lower U-values indicate better insulation. U-value = 1/R-value.
A window with U-value 0.30 is more energy-efficient than one with U-value 0.50.
Uncertainty
The range within which the true value of a measurement is expected to lie. Often expressed as a ± value.
A temperature reading of 25.0°C ± 0.5°C means the true value is between 24.5°C and 25.5°C.
Unit Conversion
The process of expressing a quantity in a different unit while maintaining the same actual value. Involves multiplying or dividing by appropriate conversion factors.
Converting 5 miles to kilometers: 5 × 1.609 = 8.045 km.
US Cup vs Metric Cup
A US cup is 236.6 mL (8 US fluid ounces); a metric cup (used in Australia, Canada) is 250 mL. This difference affects recipe accuracy.
A US recipe calling for 2 cups of water uses 473 mL, while a metric recipe uses 500 mL.
US Customary Units
The system of measurement commonly used in the United States, derived from but not identical to the British Imperial system. Key differences include volume measurements (US gallon ≠ Imperial gallon).
A US gallon equals 3.785 liters, while an Imperial gallon equals 4.546 liters.
US Gallon vs UK Gallon
A US gallon is 3.785 liters; a UK/Imperial gallon is 4.546 liters. The UK gallon is about 20% larger.
Fuel economy: 30 mpg in the UK equals about 25 mpg in US measurements.
US Pint vs UK Pint
A US pint is 473 mL (16 fl oz); a UK/Imperial pint is 568 mL (20 fl oz). UK pints are about 20% larger.
A UK pint of beer is 568 mL, while a US pint is only 473 mL.
US Tablespoon vs UK Tablespoon
A US tablespoon is 14.8 mL; a UK tablespoon is 15 mL; and an Australian tablespoon is 20 mL. Always check the recipe origin.
An Australian recipe calling for 1 tablespoon uses 4 teaspoons, not 3.
UTC
Coordinated Universal Time, the primary time standard used worldwide. Replaced GMT as the reference for time zones.
New York is UTC-5 in winter and UTC-4 in summer (daylight saving).
V
Vacuum Pressure
Pressure below atmospheric pressure. Measured as the difference between atmospheric and actual pressure, expressed in Torr, mbar, or inches of mercury.
A brake booster uses engine vacuum of about 18-22 inches of mercury.
Velocity
Speed with direction specified. Unlike speed, velocity is a vector quantity that includes both magnitude and direction.
A car traveling 60 mph north has a different velocity than one traveling 60 mph south.
Volt
The SI unit of electric potential difference, equal to one joule per coulomb of charge.
US household outlets provide 120 volts; European outlets provide 230 volts.
W
Water Column
A unit of pressure based on the height of water. Measured in inches (inH₂O) or millimeters (mmH₂O). Used for low-pressure applications like HVAC.
Natural gas pressure to homes is about 7 inches of water column.
Watt
The SI unit of power, equal to one joule per second. Measures the rate of energy transfer or conversion.
A 60-watt light bulb uses 60 joules of energy per second.
Watt-Hour
A unit of energy equal to one watt of power used for one hour (3,600 joules). Used for battery capacity.
A smartphone battery might have a capacity of 15 watt-hours.
Weight
The force exerted on an object by gravity, technically measured in Newtons. In everyday use, weight and mass are often used interchangeably.
Your weight on the Moon would be about 1/6 of your weight on Earth.
Weight vs Volume in Cooking
Weighing ingredients (grams) is more accurate than measuring by volume (cups) because volume varies with how ingredients are packed.
A cup of sifted flour weighs less than a cup of packed flour, but 120g is always 120g.
Work (Physics)
Energy transferred when a force moves an object over a distance. Calculated as force × distance, measured in joules.
Lifting a 10 kg box 2 meters requires about 196 joules of work.
Y
Yard
An imperial/US customary unit of length equal to 3 feet or 36 inches (about 0.914 meters). Used for fabric, football fields, and golf courses.
A football field is 100 yards long.