units of measurement

Units of Measurement Lists

Units of Measurement – List of SI, Imperial & US Customary Units

Units of measurement are by metrology, the scientific study of measurement. ADDucation’s units of measurement list includes Metric SI units (International System of Units), Imperial units and Unites States Customary Units (USCS). Where British, American, Canadian and Australian imperial units of volume differ we’ve included the differences.

7 SI Base Units of Measurement

The 7 Base SI Units of Measurement Defined by Fundamental Constants

  • Meter (m) length unit of measurement:
    Distance traveled by light in a vacuum in 1/299,792,458 seconds.
  • Second (s) time unit of measurement:
    9,192,631,770 cycles of radiation of an atom of caesium-133.
  • Kilogram (kg) mass unit of measurement:
    Planck’s constant divided by 6.626,070,15 × 10−34 m−2s.
  • Candela (cd) luminous intensity measurement unit:
    Light source with monochromatic radiation of frequency 540 × 1012 Hz and radiant intensity of 1/683 watt per steradian.
  • Kelvin (K) temperature unit of measurement:
    Boltzmann constant, defined as a change in thermal energy of 1.380 649 × 10−23 joules.
  • Ampere (A) electric current measurement unit:
    Flow equal to 1/1.602 176 634×10−19 elementary charges per second.
  • Mole (mol) amount of substance measurement unit:
    Avogadro constant, defined as 6.022,140,76 ×1023 elementary entities.

Base SI Units of Measurement Dependencies

  • Metre is dependent on second because its length is defined in terms of the distance traveled by light in a fraction of a second.
  • Candela and Ampere both depend on the definition of energy which is defined in terms of length (metre), mass (kilogram) and time (second).
  • Mole is dependent on kilogram because it is defined in terms of the weight of carbon atoms.
SI units of measurement chart

SI Units Dependencies Chart
Created and released by ADDucation on CC0 1.0 terms.

Key: means “equivalent to” and means “approximately equal to” using a conversion factor. ADDucation Tips: Click arrows in column headings to sort measurement units. Click the + icon to expand columns on tablets and mobiles. Set your browser to full screen and zoom out to display all units of measurement. Start typing in the Filter table box to find anything inside the table.

MeasurementUnit ofSymbolSystemFormula / Definition of Units of Measurement / Trivia
Meter/MetreLengthmMetric (SI base unit)
  • Fundamental constant definition: In 1983 the meter was defined as the distance light travels in a vacuum in 1/299,792,458th of a second.
  • Historical definitions:
    • 1960, the metre was redefined in terms of a certain number of wavelengths of a specified transition in krypton-86.
    • 1799, 1 metre was defined by a prototype metre bar located in the French National Archives (the bar was replaced in 1889).
    • 1793: 1 metre was defined as one ten-millionth of the distance from the equator to the North Pole.

One of 7 SI base units of measurement.

MillimeterLengthmmMetric0.001 m (1/1000th of a meter)
CentimeterLengthcmMetric0.01 m (1/100th of a meter)
DecimeterLengthdmMetric0.1 m (1/10th of a meter)
KilometerLengthkmMetric1000 meters (or 0.62137 mile or 3,280.8 feet)
Astronomical UnitLengthAEMetric1,49598 x 1011 m
Light YearLengthljMetric9,4505 x 1015 m
ParsecLengthpcMetric3,0857 x 1016 m
InchLengthin or “Imperial / USCS1 inch = 2.54 cm or 25.4 mm
FootLengthftImperial / USCS12 inches (or 30.48 cm or 304.8 mm)
YardLengthydImperial / USCS3 feet or 36 inches (or 91.44 cm or 914.4 mm). The international yard is defined as exactly 0.9144 metres so it is effectively one of the fundamental Imperial units of measurement.
MileLengthmiImperial / USCS1,760 yards or 5,280 feet (or 1609 m or 1.61 km)
Nautical MileLengthsmImperialexactly 1,852 meters (or about 6,076 feet)
Square meterAreasqm or m2Metric (derived)1 square meter = 10,000 cm2 = 1,000,000 mm2
AcreAreaacreImperial / USCS1 acre 43560 sq ft = 4046.873 m2 and 0.405 hectare
AreAreaa or aresMetric (derived)1 are = 100 m² ≡ 0.0247 acre. 100 ares = 1 hectare, the most common unit of land measurement in the world.
HectareAreahaMetric1 ha = 100 ares which is 10,000 m2 and ≡ 2.47 acres
Square inchesAreain2Imperial1 square inch = 6.4516 cm2
Square feetAreaft2Imperial1 square foot = 144 square inches (12″ x 12″) = 0.093 m2
Square yardsAreayd2Imperial1 square yard = 9 square feet = 0.836 m2
Square milesAreami2Imperial1 square mile = 2.59 km2
Cubic meterVolume (V)m3Metric1m x 1m x 1m = m3 The original metric system included stere (stère) as a unit of volume for firewood.
LiterVolume (V)lMetric(rough guide: 1 liter of water weighs approximately 1kg at 4ºC)
MilliliterVolume (V)mlMetric1 cm3 ≡ 0,001 liter
CentiliterVolume (V)clMetric0,01 l ≡ 10 ml
DeciliterVolume (V)dlMetric0,1 l ≡ 100 ml
HectoliterVolume (V)hlMetric100 liters
Cubic InchVolume (V)cu in or in3USCS1 Cubic Inch 16.387 ml
Cubic FootVolume (V)cu ft or ft3USCS1 Cubic Foot = 1,728 cu in and 28.317
Cubic YardVolume (V)cu yd or yd3USCS1 Cubic Yard = 27 cu ft and 764.555 or 0.7645m3
Acre-FootVolume (V)acre ftUSCSI Acr -Foot = 43560 cu ft and 1233.48m3
TeaspoonVolume (V)tspImperial / USCS
  • UK: 1 imperial teaspoon ≈ 1.20095 US teaspoon ≈ 5.91939 ml
  • US: 1 US teaspoon ≡ 13 US tablespoon ≡ 16 US fluid ounce and ≈ 0.83 imperial teaspoon ≈ 4.93 ml
TablespoonVolume (V)tbspImperial / USCS
  • UK: 1 imperial tablespoon ≈ 1.20095 US tablespoon ≈ 17.7582 ml
  • US: 1 US tablespoon ≡ 3 US teaspoons ≡ 12 US fluid ounce and ≈ 0.832674 imperial tablespoon ≈ 14.8 ml
  • Australia: 1 Australian tablespoon ≈ 20 ml
  • Canada: 1 Canadian tablespoon ≈ 15 ml
Fluid ounceVolume (V)fl oz or oz. flImperial / USCS
  • UK: 1 imperial fluid ounce ≡ 1160 imperial gallon 120 imperial pint ≡ 15 imperial gill and ≈ 28.41 mm3 ≈ 1.73 cubic inches ≈ 0.96 US fluid ounces
  • US: 1 US fluid ounce ≡ 1128 US gallon ≡ 116 US pint ≡ 14 US gill ≡ 2 US tablespoons ≡ 6 US teaspoons and ≈ 1.04 imperial fluid ounces ≈ 29.57 ml
CupVolume (V)cupImperial / USCS
  • UK: 1 cup ≡ 284.13 ml
  • USA: 1 cup ≡ 236.59 ml
  • Australia/Canada: ≡ 250 ml
GillVolume (V)gillImperial / USCS
  • UK: 1 imperial gill ≡ 14 imperial pint ≡ 5 imperial fluid ounces and ≈ 1.2 US gills ≈ 142 ml
  • US: 1 US liquid gill ≡ 14 US liquid pint ≡ 4 US fluid ounces ≡ 1⁄32 US gallon and ≈ 5⁄6 imperial gills = 118 ml
  • US: 1 US dry gill = 138 ml
PintVolume (V)pt or pImperial / USCS
  • UK: 1 imperial pint ≡ 18 imperial gallon ≡ 4 imperial gills ≡ 20 imperial fluid ounces and ≈ 1.2 US liquid pints ≈ 568 ml
  • US: 1 US liquid pint ≡ 18 US liquid gallon ≡ 16 US fluid ounces and ≈ 0.83 imperial pints ≈ 473 ml
  • US: 1 US dry pint ≡ 18 US dry gallons ≡ 33.6 cubic inches and ≈ 0.97 imperial pints ≈ 551 ml
QuartVolume (V)qtImperial / USCS
  • UK: 1 imperial quart ≡ 14 imperial gallon ≡ 40 imperial fluid ounces and ≈ 1.14 litres ≈ 38.43 US fluid ounces
  • US: 1 US liquid quart ≡ 14 US liquid gallon ≡ 32 US fluid ounces and ≈ 33 imperial fluid ounces ≈ 946 ml
  • US: 1 US dry quart ≡ 14 US dry gallon ≡ 67.2 cubic inches and ≈ 38.76 imperial fluid ounces ≈ 1101 ml
GallonVolume (V)galImperial / USCS
  • UK: 1 imperial gallon was defined in 1824 as the volume of 10 pounds of water at 62°F and ≡ 8 imperial pints ≡ 160 imperial fluid ounces ≡ 4.55 liters and ≈ 1.2 US gallons
  • US: 1 US liquid gallon ≡ 8 US pints ≡ 16 US fluid ounces ≡ 3.78 liters and ≈ 0.83 imperial gallons
  • US: 1 US dry gallon ≡ 268.8 cubic inches ≈ 4.4 liters. Not used in commerce.
RadianAngle (α)rad or cMetric (derived)1 rad = 57.295° (2Π radians = 360 degrees, which is a circle)
DegreeAngle (α)° or degMetricΠ/180° = 0.01745329 rad (1 degree = Π/180 radians)
SteradianSolid angle (Ω)srMetric (derived)A steradian is (180/Π)2 square degrees (about 3282.8 square degrees)
SecondTime (t)sMetric (SI base unit)1 second = 9,192,631,770 cycles of radiation of an atom of Cs-133 transition (the period required by electrons flitting between 2 energy levels in a Caesium isotope). One of 7 SI base units of measurement.
MinuteTime (t)minMetric (derived)60 seconds
HourTime (t)hMetric (derived)60 min ≡ 3,600 seconds
DayTime (t)dMetric (derived)24 hours ≡ 1,440 minutes or 86,400 seconds
YearTime (t)aMetric (derived)365.24 days
HertzFrequency (f)HzMetric (derived)One cycle per second: 1/s or s−1
Angular FrequencyFrequency (f)ωMetricRadians per secound. 1 x s-1 ≡ 60 x min-1
DecibelSounddBMetricLogarithmic unit to describe a ratio which could be intensity, power, sound pressure, voltage or in common usage loudness.
Kilogram meters per secondMomentumkg m/sMetricMomentum = Mass x Velocity. The derived unit is newton second.
Miles per hourSpeedmphImperialDistance divided by time
Meters per secondSpeedm/s or kphMetricDistance divided by time
Gravity Imperial
Acceleration of Gravity (g)ft/s2Imperial1 g = 32.174 ft/s2 = 386.1 in/s2 = 22 mph/s
Gravity MetricAcceleration of Gravity (g)m/s2Metric1 g = 9.81 m/s2 = 35.30394 (km/h)/s
Feet per secondMassft/sImperial
GramsMassgMetric (derived)1000 grams = 1 kg or 1 gram = 0.001 kg. The original metric system included “gramme” as the unit of mass for 1 cubic centimeter of water but was quickly deemed too small. The “kilo” prefix was added resulting in “kilogramme”.
Kilogram
MasskgMetric (SI base unit)
  • Fundamental constant definition (effective from World Metrology Day May 2019): Planck’s constant divided by 6.626,070,15 × 10−34 m−2s.
  • International Prototype Kilogram (IPK aka Le Grande K and Big K): 1 kilogram = 1000g and is the mass of an international kilogram prototype, a cylinder made from a platinum-iridium alloy, which weighs ≈ 2.2 pounds.

One of 7 SI base units of measurement. The kilogram is the only SI base unit with an SI prefix (see Grams).

GrainMassgrImperial / USCS1 Grain = 1⁄7000 lb and ≈ 0.0648 g or 64.8 mg
DramMassdrImperial / USCS1 Dram = 27 11⁄32 gr and ≈ 1.77 g
OunceMassozImperial1 Ounce = 1/16 pound or 16 dr ≈ 28.35 g
PoundMasslbImperial / USCS1 Pound = 16 oz ≈ 0.45 kg. The pound is one of the fundamental Imperial units of measurement.
HundredweightMasscwtImperial / USCS
  • UK: 8 stone or 112 lb (50.80234544 kg) long ton (2240 lb, 1016.0469088 kg) 2o hundredweights make a ton.
  • US: 100 lb (45.359237 kg) short ton (2000 lb; 907.18474 kg) 2o hundredweights make a ton.
TonMasstonImperial / USCS
  • UK: 2240 lb ≡ 20 (UK) hundredweight 1016.047 kg (aka long ton, weight ton, gross ton, ton shortweight).
  • US (and formerly Canada): 2000 lb ≡ 20 (US) hundredweight 907.1847 kg (aka short ton, net ton).
Tonne
MasstMetric1000 kg 2204.622 lb (aka a metric ton in the USA).
SlugMassslugUSCS1 slug = 1 lbf·s2/ft (A mass that accelerates by 1 ft/s2 when a force of one pound (lbf) is exerted on it).
DensityDensity (ρ)kg/m3MetricDensity = mass divided by volume in kilogram per cubic meter (kg/m3).
NewtonForce, Weight (F)NMetric (derived)Named after Sir Isaac Newton. Kg and m/s2
KilopondForce (F)kpMetric9.80665 Newtons
PondForce (F)pMetric9,80665 x 10-3 Newtons
Newton meterTorque (M)MetricN x m = kg x m2 x s-2
JouleWork, Energy (E)JMetric (derived)N x m = W x s = kg x m2 x s-2
WattPower, Radiant Flux (P)wMetric (derived)J x s-1 = kg x m2 x s-3
KilowattPower (P)kwMetric1 Kilowatt ≡ 1,000 Watts
HorsepowerPower (P)hpDeprecated1 horsepower equates to the power required to lift 75 kg 1 meter in 1 second which is 735.5w. Horsepower is officially obsolete but still in common usage.
PascalPressure, StressPaMetric (derived)One newton per square metre. Named after Blaise Pascal.
BarPower (P)barMetric1 bar ≡ 105 Pa
Pounds per square inchPressurepsi or lbf/in2Imperial1 psi ≈ 6894.8 Pascal or 0.0689 Bar
KelvinTemperature (T)KMetric (SI)
  • Fundamental constant definition: The Boltzmann constant. Change in thermal energy of 1.380 649 × 10−23 joules.
  • Historical definition: One Kelvin is 1/273.16 of the thermodynamic temperature of the triple point of water (at which water vapor, ice and water co-exist in equilibrium) 0.0036609°C

One of 7 SI base units of measurement.

CentigradeTemperature (T)°CMetric (derived)0°C is the freezing point of water. Absolute zero is -273.15°C or 0 Kelvin.
CalorieAmount of Heat (Q)Cal or kcal / calMetric1 Thermochemical calorie = 4.1868 Joules. There are two common uses:
  • 1 large calorie (Cal or kcal) is commonly used to indicate calories in food and by nutritionists. It’s roughly the amount of energy needed to increase the temperature of 1 kg of water by 1°C
  • 1 small or gram calorie (cal) is roughly the amount of energy needed to increase the temperature of one gram of water by 1°C
FahrenheitTemperature (T)°FImperial / USCSTemperature scale on which water freezes at 32°F and boils at 212°F under standard conditions.
CandelaLuminous Intensity (l)cdMetric (SI base unit)
  • Historical definition: One Candela = the light from one candle.
  • Fundamental constant definition (taking into account the color of the light and its direction): Light source with monochromatic radiation of frequency 540 × 1012 Hz (cycles per second in Hertz) and radiant intensity of 1/683 watt per steradian. The color is yellowish green, which the human eye distinguishes really well.

One of 7 SI base units of measurement.

Candela per square metreLuminance (L)cd/m2Metric (derived)The intensity of light emitted from a surface per unit area in a given direction.
LumenLuminous Flux (Φ)lmMetric (derived)cd x sr. A lumen is the measure of the total amount of visible light emitted from a source, taking into account the beam and angle.
LuxIlluminance (E)lxMetric (derived)One lumen per square metre. lm x s = cd x sr x m-2
Lumen SecondsLight quantity (Q)lsMetriclm x s
DiopterRefractive Index (D)dptMetric1 x m-1
AmpereCurrent (I)A / AmpsMetric (SI base unit)Ampere is used to express the flow rate of electric charge.
  • Historical definition: 1 ampere equates to a flow of one coulomb per second.
  • Fundamental constant definition: Flow equal to 1/1.602 176 634×10−19 elementary charges per second.

One of 7 SI base units of measurement.

CoulombElectric Charge (Q)CMetric (derived)Charge carried by a constant current of one ampere in one second.
VoltVoltage, Electrical (U)VMetric (derived)Potential difference in charge expressed as a ratio between two points in an electrical field. W x A-1 = kg x m2 x (s3 x A)-1
OhmElectrical Resistance, Impedence (R)ΩMetric (derived)W x A-1 = kg x m2 x (s3 x A2)-1
(Mnemonic to remember the order of color coding on resistors)
FaradElectrical Capacitance (F)FMetric (derived)One farad is the capacitance across which, when charged with one coulomb, has a potential difference of one volt. Named after Michael Faraday.
SiemensElectrical Conductance (S)SMetric (derived)One Siemens is equal to the reciprocal of one ohm. Named after Ernst Werner von Siemens.
HenryElectrical Inductance (H)HMetric (derived)The inductance of a closed circuit in which an electromotive force of one volt is produced when the electric current in the circuit varies uniformly at a rate of one ampere per second. Named after Joseph Henry.
WeberMagnetic Flux (Wb)WbMetric (derived)A change in flux of one Weber per second induces an electromotive force of one volt. Named after Wilhelm Eduard Weber.
TeslaMagnetic Flux Density, Magnetic Field (T)(T)Metric (derived)One tesla is equal to one Weber per square metre. Named after Nikola Tesla.
BecquerelRadioactive DecayBqMetric (derived)Bq = 1 x s-1
MoleAmount of Substance (s)molMetric (SI base unit)One mole is the number of atoms in 12 thousandths of a kilogram of carbon C-12.
  • Fundamental constant definition: The number expressed by the Avogadro constant is defined as 6.022,140,76 ×1023 elementary entities.

One of 7 SI base units of measurement.

Paper BalePaper QuantityreamImperial1 ream = 500 sheets of paper
DozenQuantitiesdz or dozImperial12 items, eggs are commonly sold as half a dozen or a dozen. A bakers dozen is 13 items, 12+1 to be sure they were not underweight.
United States Customary Units of Measurement

US Customary Units of Measurement

By 1893 most United States customary units were redefined using the metric system meter and kilogram units, which evolved into the International System of Units (SI), preferred by the US National Institute of Standards and Technology (NIST) and used for most new units of measure or mixed with US customary units.

Key Facts & Differences Between US & Imperial Units

Key Differences Between Imperial and USC Units

  • Length:
    Conversion between Imperial and USC Units of measurement for length is based on 1959 International Yard and Pound Agreement between the USA, Canada, the United Kingdom, Australia, New Zealand and South Africa which defines the international yard as exactly 0.9144 metres.
  • Volume:
    • Imperial and US Customary Units of measurement based on cubic length (cubic inch, cubic foot etc) are the SAME.
    • Imperial and US Customary Units of measurement for specific volume units (bushel, gallon, fluid ounce etc) are DIFFERENT.
    • USC units of measurement for volumes are DIFFERENT for fluids and dry goods:
    • Imperial units of measurement for specific volumes are the SAME for fluids and dry goods.
    • Imperial and USC units of measurement for volumes EVEN WITH THE SAME NAMES are DIFFERENT specifically (teaspoon, tablespoon, cup fluid ounce, gill, pint, quart and gallon).
    • USC units of measurement for DRY volumes (gallons, quarts, pints, gills) are approximately 3.3% smaller than the equivalent Imperial volume units of measurement.
    • USC units of measurement for FLUID volumes (gallons, quarts, pints and gills are about 20% smaller than the equivalent Imperial volume units of measurement BUT Imperial fluid ounces are approximately 4% smaller than US fluid ounces.
    • Canada uses a mixture of both systems which causes labeling confusion for units of measurement on bottles and cans.
  • Weight & Mass:
    Historically there are three different weight systems, all based on fractions or multiples of the pound (lb):
    • Troy weight; for precious metals
    • Apothecaries’ weight; for medicines, now mostly superseded by metric units of measurement.
    • Avoirdupois weight; most other purposes
Why Are Imperial & USC Units of Measurement Different?

Imperial & USC Units of Measurement Are Different Because…

In 1824 various different volume units of measurement, in use across the British Empire, were replaced with a single system based on the Imperial gallon. The US continued to use the “obsolete” Winchester measure and formally adopted it in 1836 to define the US dry gallon. The US fluid gallon was defined as 231 cubic inches. Both Imperial and USC units sub-divide a gallon into four quarts, eight pints and 32 gills.
The US gill is divided into four US fluid ounces but the Imperial gill is divided into five Imperial fluid ounces. This leads to confusion when converting sub-divisions of fluid ounces.

How Do Differences Between Imperial & US Units Affect YOU?

How the Differences Between Imperial & US Units Affect YOU:

  • Body Weights: In the US body weight is measured in pounds, in the UK, and some other countries, body weight is still typically measured in stones and pounds (or kilograms).
  • Drivers: When comparing gas/petrol prices, or calculating miles per gallon (MPG), make sure you use the appropriate US Gallon to Imperial Gallons (or Litres) conversion.
  • Cooks/Chefs: When using recipes which include teaspoons, tablespoons and cups units of measurement to check whether the units of measurement are US or Imperial.
  • Buying heavy items: UK and US tons (and hundredweights) are different and there’s also a metric tonne (metric ton). The difference between the heaviest (UK) and lightest (US) is 11%.

More ADDucation Lists Related to Units of Measurement:


2 responses to “Units of Measurement Lists”

  1. Kusuma C says:

    Superb useful info.

  2. Suresh.s says:

    So good

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