Units of Measurement List


All Units of Measurement List SI, Imperial & USC Units

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

  • ADDucation’s list of all units of measurement was last updated 25 Sep 2024

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List of units Unit of Symbol System Formula / Definition of Units of Measurement / Trivia
Meter/Metre Length m Metric

(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.
Millimeter Length mm Metric 0.001 m (1/1000th of a meter).
Centimeter Length cm Metric 0.01 m (1/100th of a meter).
Decimeter Length dm Metric 0.1 m (1/10th of a meter).
Kilometer Length km Metric 1000 meters (or 0.62137 mile or 3,280.8 feet).
Inch Length in or “ Imperial / USCS 1 inch = 2.54 cm or 25.4 mm.
Foot Length ft Imperial / USCS 12 inches (or 30.48 cm or 304.8 mm).
  • The international foot is a exactly 0.3048 meters
  • US Survey Foot is a fraction: 1200/3937 meters, a difference of one one-hundredth of a foot per mile
Yard Length yd Imperial / USCS 3 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.
Rod/Perch / Pole/Lug
 Length Imperial / USCS 1 rod is 16 1⁄2 US survey feet = 5.0292 m. To convert US feet to international feet multiply by 1.000002000004000008000016000032
Chain Length Imperial / USCS 1 chain = 66 feet (22 yards) = 20.1168 meters.
1 chain = 4 rods or 100 links. 10 chains = 1 furlong. 80 chains = 1 international/statute mile.
The distance between the stups on a cricket pitch is still defined as one chain.
Furlong Length Imperial / USCS 1 furlong is 1⁄8 of a mile. One furlong = 220 yards ≡ 201.1680 meters. Race lengths in furlongs are still used in many countries, most noteably horse racing.
Mile Length mi or m or ml Imperial / USCS 1,760 yards or 5,280 feet. In 1959, by international agreement, one mile was standardized as exactly 1,609.344 metres. 1 square mile is 640 acres.
Nautical Mile Length sm Imperial exactly 1,852 meters (or about 6,076 feet).
Astronomical Unit Length AE Metric 149,597,870,700 m (or 1.49598 x 1011 m).
Light Year Length lj Metric 9.4607 x 1015 m (or 9.4607 Pm)
Parsec Length pc Metric 3.0857 x 1016 m.
Square meter Area sqm or m2 Metric (derived) 1 square meter = 10,000 cm2 = 1,000,000 mm2
Hectare Area ha Metric 1 ha = 100 ares which is 10,000 m2 and ≡ 2.47 acres.
Square inch Area in2 Imperial 1 square inch = 6.4516 cm2
Square feet Area ft2 Imperial 1 square foot = 144 square inches (12″ x 12″) = 0.093 m2
Square yard Area yd2 Imperial 1 square yard = 9 square feet = 0.836 m2
Square mile Area sq mi or mi2 Imperial / USCS 1 square mile = 2.59 km2 or 27,878,400 ft2
Cubic meter Volume (V) m3 Metric 1m x 1m x 1m = m3 The original metric system included stere (stère) as a unit of volume for firewood.
Liter Volume (V) l Metric (rough guide: 1 liter of water weighs approximately 1kg at 4 ºC).
Milliliter Volume (V) ml Metric 1 cm3 ≡ 0,001 liter.
Centiliter Volume (V) cl Metric 0,01 l ≡ 10 ml.
Deciliter Volume (V) dl Metric 0,1 l ≡ 100 ml.
Hectoliter Volume (V) hl Metric 100 liters.
Cubic Inch Volume (V) cu in or in3 USCS 1 Cubic Inch ≈16.387 ml.
Cubic Foot Volume (V) cu ft or ft3 USCS 1 Cubic Foot = 1,728 cu in and ≈ 28.317.
Cubic Yard Volume (V) cu yd or yd3 USCS 1 Cubic Yard = 27 cu ft and ≈ 764.555 or 0.7645m3
Acre-Foot Volume (V) acre ft USCS 1 Acr -Foot = 43560 cu ft and ≈ 1233.48m3
Teaspoon Volume (V) tsp Imperial / USCS
  • UK: 1 Imperial teaspoon ≈ 1.20095 US teaspoon ≈ 5.91939 ml
  • US: 1 US teaspoon ≡ 1⁄3 US tablespoon ≡ 1⁄6 US fluid ounce and ≈ 0.83 imperial teaspoon ≈ 4.93 ml
Tablespoon Volume (V) tbsp Imperial / USCS
  • UK: 1 imperial tablespoon ≈ 1.20095 US tablespoon ≈ 17.7582 ml
  • US: 1 US tablespoon ≡ 3 US teaspoons ≡ 1⁄2 US fluid ounce and ≈ 0.832674 imperial tablespoon ≈ 14.8 ml
  • Australia: 1 Australian tablespoon ≈ 20 ml
  • Canada: 1 Canadian tablespoon ≈ 15 ml
Fluid Ounce Volume (V) fl oz or oz. fl Imperial / USCS
  • UK: 1 imperial fluid ounce ≈ 28.4130625 ml
    (1 imperial fluid ounce ≡ 1⁄160 imperial gallon or 1⁄20 imperial pint ≡ 1⁄5 imperial gill ≈ 1.73 cubic inches ≈ 0.9588 US fluid ounces)
    To convert UK fluid ozs to ml multiply 28.4130625
    To convert ml to UK fluid ounces multiply by 0.03519507972 or divide by 28.4130625
    To convert imperial fluid ounces to US fluid ounces multiply by 0.9588 or divide by 1.043
  • US: 1 US fluid ounce ≈ 29.5735296 ml.
    (1 US fluid ounce ≡ 1⁄128 US gallon ≡ 1⁄16 US pint ≡ 1⁄4 US gill ≡ 2 US tablespoons ≡ 6 US teaspoons and ≈ 1.04 imperial fluid ounces)
    To convert US fluid ozs to ml multiply 29.5735296
    To convert ml to US fluid ounces multiply by 0.033814 or divide by 29.5735296
    To convert US fluid ounces to UK fluid ounces multiply by 1.043 or divide by 0.9588.
Cup Volume (V) cup Imperial / USCS
  • UK: 1 cup ≡ 284.13 ml
  • USA: 1 cup ≡ 236.59 ml
  • Australia/Canada: ≡ 250 ml.
Gill Volume (V) gill Imperial / USCS
  • UK: 1 imperial gill ≡ 1⁄4 imperial pint ≡ 5 imperial fluid ounces and ≈ 1.2 US gills ≈ 142 ml
  • US: 1 US liquid gill ≡ 1⁄4 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.
Pint Volume (V) pt or p Imperial / USCS
  • UK: 1 imperial pint ≡ 1⁄8 imperial gallon ≡ 4 imperial gills ≡ 20 imperial fluid ounces and ≈ 1.2 US liquid pints ≈ 568 ml
  • US: 1 US liquid pint ≡ 1⁄8 US liquid gallon ≡ 16 US fluid ounces and ≈ 0.83 imperial pints ≈ 473 ml
  • US: 1 US dry pint ≡ 1⁄8 US dry gallons ≡ 33.6 cubic inches and ≈ 0.97 imperial pints ≈ 551 ml.
Quart Volume (V) qt Imperial / USCS
  • UK: 1 imperial quart ≡ 1⁄4 imperial gallon ≡ 40 imperial fluid ounces and ≈ 1.14 litres ≈ 38.43 US fluid ounces
  • US: 1 US liquid quart ≡ 1⁄4 US liquid gallon ≡ 32 US fluid ounces and ≈ 33 imperial fluid ounces ≈ 946 ml
  • US: 1 US dry quart ≡ 1⁄4 US dry gallon ≡ 67.2 cubic inches and ≈ 38.76 imperial fluid ounces ≈ 1101 ml.
Gallon Volume (V) gal Imperial / 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.
Radian Angle (α) rad or c Metric (derived) 1 rad = 57.295° (2Π radians = 360 degrees, which is a circle).
Degree Angle (α) ° or deg Metric Π/180° = 0.01745329 rad (1 degree = Π/180 radians).
Steradian Solid angle (Ω) sr Metric (derived) A steradian is (180/Π)2 square degrees (about 3282.8 square degrees).
Second Time (t) s Metric

(SI base unit)

 1 second = 9,192,631,770 cycles of radiation of an atom of Cs-133 transition.
Minute Time (t) min Metric (derived) 60 seconds.
Hour Time (t) h Metric (derived) 60 min ≡ 3,600 seconds.
Day Time (t) d Metric (derived) 24 hours ≡ 1,440 minutes or 86,400 seconds.
Year Time (t) a Metric (derived) 365.24 days.
Hertz Frequency (f) Hz Metric (derived) One cycle per second: 1/s or s−1
Angular Frequency Frequency (f) ω Metric Radians per second. 1 x s-1 ≡ 60 x min-1
Decibel Sound dB Metric Logarithmic unit to describe a ratio which could be intensity, power, sound pressure, voltage or in common usage loudness.
Kilogram meters per second Momentum kg m/s Metric Momentum = Mass x Velocity. The derived unit is newton second.
Miles per hour Speed mph Imperial Distance divided by time.
Meters per second Speed m/s or kph Metric Distance divided by time.
Gravity Imperial
 Acceleration of Gravity (g) ft/s2 Imperial 1 g = 32.174 ft/s2 = 386.1 in/s2 = 22 mph/s.
Gravity Metric Acceleration of Gravity (g) m/s2 Metric 1 g = 9.81 m/s2 = 35.30394 (km/h)/s.
Feet per second Mass ft/s Imperial
Grams Mass g Metric (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
 Mass kg Metric

(SI base unit)
  • Fundamental constant definition: 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.
Grain Mass gr Imperial / USCS 1 Grain = 1⁄7000 lb and ≈ 0.0648 g or 64.8 mg.
Dram Mass dr Imperial / USCS 1 Dram = 27 11⁄32 gr and ≈ 1.77 g.
Ounce Mass oz Imperial 1 Ounce = 1/16 pound or 16 dr ≈ 28.35 g.
Pound Mass lb Imperial / USCS 1 Pound = 16 oz ≈ 0.45 kg. The pound is one of the fundamental Imperial units of measurement.
Hundredweight Mass cwt Imperial / 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.
Ton Mass ton Imperial / 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
 Mass t Metric 1000 kg ≈ 2204.622 lb (aka a metric ton in the USA).
Slug Mass slug USCS 1 slug = 1 lbf·s2/ft (A mass that accelerates by 1 ft/s2 when a force of one pound (lbf) is exerted on it).
Density Density (ρ) kg/m3 Metric Density = mass divided by volume in kilogram per cubic meter (kg/m3).
Newton Force, Weight (F) N Metric (derived) Named after Sir Isaac Newton. Kg and m/s2
Kilopond Force (F) kp Metric 9.80665 Newtons
Pond Force (F) p Metric 9,80665 x 10-3 Newtons
Newton meter Torque (M) Metric N x m = kg x m2 x s-2
Joule Work, Energy (E) J Metric (derived) N x m = W x s = kg x m2 x s-2
Watt Power, Radiant Flux (P) w Metric (derived) J x s-1 = kg x m2 x s-3
Kilowatt Power (P) kw Metric 1 Kilowatt ≡ 1,000 Watts.
Horsepower Power (P) hp Traditional 1 horsepower equates to the power required to lift 75 kg 1 meter in 1 second which is 735.5w.
Pascal Pressure, Stress Pa Metric (derived) One newton per square metre. Named after Blaise Pascal.
Bar Power (P) bar Metric The bar is a metric unit of pressure (but not an SI unit). 1 bar= 100,000 Pa (1 bar = 105 Pa which is slightly less than current average atmospheric pressure on Earth at sea level.

 
Pounds per square inch Pressure psi or lbf/in2 Imperial Pound-force per square inch (lbf/in2). PSI is a measure of force per unit area. 1 psi ≈ 6894.8 Pascal or 0.0689 Bar.
Kelvin Temperature (T) K Metric (SI)

(base SI unit)
  • 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.
Centigrade Temperature (T) °C Metric (derived) 0 °C is the freezing point of water. Absolute zero is -273.15 °C or 0 Kelvin.
Calorie Amount of Heat (Q) Cal or kcal / cal Metric 1 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.
Fahrenheit Temperature (T) °F Imperial / USCS A measure of temperature based on the Fahrenheit scale proposed by physicist Daniel Gabriel Fahrenheit in 1724. On the Farenheit scale water freezes at 32 °F and boils at 212 °F under standard conditions. A rough rule of thumb to convert Farenheit to Centigrade is to subtract 30 then divide by 2 (or multiply by 2 and add 30 to convert °C to °F).
Candela Luminous Intensity (l) cd Metric

(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.
Candela per square metre Luminance (L) cd/m2 Metric (derived) The intensity of light emitted from a surface per unit area in a given direction.
Lumen Luminous Flux (Φ) lm Metric (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.
Lux Illuminance (E) lx Metric (derived) One lumen per square metre. lm x s = cd x sr x m-2
Lumen Seconds Light quantity (Q) ls Metric lm x s
Diopter Refractive Index (D) dpt Metric 1 x m-1
Ampere Current (I) A / Amps Metric

(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.
Coulomb Electric Charge (Q) C Metric (derived) Charge carried by a constant current of one ampere in one second.
Volt Voltage, Electrical (U) V Metric (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
Ohm Electrical Resistance, Impedance (R) Ω Metric (derived) W x A-1 = kg x m2 x (s3 x A2)-1
(Mnemonic to remember the order of color coding on resistors)
Farad Electrical Capacitance (F) F Metric (derived) One farad is the capacitance across which, when charged with one coulomb, has a potential difference of one volt. Named after Michael Faraday.
Siemens Electrical Conductance (S) S Metric (derived) One Siemens is equal to the reciprocal of one ohm. Named after Ernst Werner von Siemens.
Henry Electrical Inductance (H) H Metric (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.
Weber Magnetic Flux (Wb) Wb Metric (derived) A change in flux of one Weber per second induces an electromotive force of one volt. Named after Wilhelm Eduard Weber.
Tesla Magnetic Flux Density, Magnetic Field (T) (T) Metric (derived) One tesla is equal to one Weber per square metre. Named after Nikola Tesla.
Becquerel Radioactive Decay Bq Metric (derived) Bq = 1 x s-1
Mole Amount of Substance (s) mol Metric

(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.
Paper Bale Paper Quantity ream Imperial 1 ream = 500 sheets of paper.
Dozen Quantities dz or doz Imperial 12 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.

See also: List of Commonly Used Abbreviations (acronyms)…

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