**Meter/Metre**LengthmMetric (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.

**Millimeter**LengthmmMetric0.001 m (1/1000th of a meter).

**Centimeter**LengthcmMetric0.01 m (1/100th of a meter).

**Decimeter**LengthdmMetric0.1 m (1/10th of a meter).

**Kilometer**LengthkmMetric1000 meters (or 0.62137 mile or 3,280.8 feet).

**Inch**Lengthin or “Imperial / USCS1 inch = 2.54 cm or 25.4 mm.

**Link**

(Gunter’s link)

**Lengthl., li. or lnk.Imperial / USCS1 link = 0.01 chain = 0.04 rod = 0.66 foot = 0.22 yard = 7.92 inches ≡ 0.201168 meters.**

Gunter’s chain, designed by Edmund Gunter in 1620 in England, was a metal chain made up of 100 links. Each link is

^{66}⁄

_{100}of a US survey foot, or exactly 7.92 inches. The link was widely used in surveying in English speaking countries until the 20th century.

- Twenty-five links make a rod
- One hundred links make a chain
- One thousand links make a furlong
- Eight thousand links make a mile.

**Foot**LengthftImperial / USCS12 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**LengthydImperial / 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.

**Rod/Perch / Pole/Lug**

LengthImperial / USCS1 rod is 16

^{1}⁄

_{2}US survey feet = 5.0292 m. To convert US feet to international feet multiply by 1.000002000004000008000016000032

**Chain**LengthImperial / USCS1 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**LengthImperial / USCS1 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**Lengthmi or m or mlImperial / USCS1,760 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**LengthsmImperialexactly 1,852 meters (or about 6,076 feet).

**Astronomical Unit**LengthAEMetric149,597,870,700 m (or 1.49598 x 10

^{11 }m).

**Light Year**LengthljMetric9.4607 x 10

^{15 }m (or 9.4607 Pm)

**Parsec**LengthpcMetric3.0857 x 10

^{16}m.

**Square meter**Areasqm or m

^{2}Metric (derived)1 square meter = 10,000 cm

^{2}= 1,000,000 mm

^{2}

**Are**Areaa or aresMetric (derived)1 are = 100 m² ≡ 0.0247 acre. 100 ares = 1 hectare, the most common unit of land measurement in the world.

**Acre**AreaacreImperial / USCS1 acre 43560 sq ft = 4046.873 m

^{2}and

**≡**0.405 hectare. There are 640 acres in 1 square mile.

In Imperial units (before 1 Jan 1964 and USCS units a “perfect acre” is also a rectangular area of 43,560 square feet, bounded by sides 660 feet (a furlong) long and 66 feet wide, which is also equivalent to: 220 yards by 22 yards (a chain) or 40 rods by 4 rods. Therefore an acre is equivalent to 160 square rods or 10 square chains.

**Hectare**AreahaMetric1 ha = 100 ares which is 10,000 m

^{2}and ≡ 2.47 acres.

**Square inch**Areain

^{2}Imperial1 square inch = 6.4516 cm

^{2}

**Square feet**Areaft

^{2}Imperial1 square foot = 144 square inches (12″ x 12″) = 0.093 m

^{2}

**Square yard**Areayd

^{2}Imperial1 square yard = 9 square feet = 0.836 m

^{2}

**Square mile**Areasq mi or mi

^{2}Imperial / USCS1 square mile = 2.59 km

^{2}or 27,878,400 ft

^{2}

**Cubic meter**Volume (V)m

^{3}Metric1m x 1m x 1m = m

^{3 }The original metric system included stere (stère) as a unit of volume for firewood.

**Liter**Volume (V)lMetric(rough guide: 1 liter of water weighs approximately 1kg at 4 ºC).

**Milliliter**Volume (V)mlMetric1 cm

^{3}≡ 0,001 liter.

**Centiliter**Volume (V)clMetric0,01 l ≡ 10 ml.

**Deciliter**Volume (V)dlMetric0,1 l ≡ 100 ml.

**Hectoliter**Volume (V)hlMetric100 liters.

**Cubic Inch**Volume (V)cu in or in

^{3}USCS1 Cubic Inch

**≈**16.387 ml.

**Cubic Foot**Volume (V)cu ft or ft

^{3}USCS1 Cubic Foot = 1,728 cu in and

**≈**28.317.

**Cubic Yard**Volume (V)cu yd or yd

^{3}USCS1 Cubic Yard = 27 cu ft and

**≈**764.555 or 0.7645m

^{3}

**Acre-Foot**Volume (V)acre ftUSCS1 Acr -Foot = 43560 cu ft and

**≈**1233.48m

^{3}

**Teaspoon**Volume (V)tspImperial / 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)tbspImperial / 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. flImperial / 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)cupImperial / USCS

- 🇬🇧
**UK**: 1 cup ≡ 284.13 ml - 🇺🇸
**USA**: 1 cup ≡ 236.59 ml - 🇦🇺🇨🇦
**Australia/Canada**: ≡ 250 ml.

**Gill**Volume (V)gillImperial / 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 pImperial / 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)qtImperial / 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)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.

**Radian**Angle (α)rad or

^{c}Metric (derived)1 rad = 57.295° (2Π radians = 360 degrees, which is a circle).

**Degree**Angle (α)° or degMetricΠ/180° = 0.01745329 rad (1 degree = Π/180 radians).

**Steradian**Solid angle (Ω)srMetric (derived)A steradian is (180/Π)

^{2}square degrees (about 3282.8 square degrees).

**Second**Time (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.

**Minute**Time (t)minMetric (derived)60 seconds.

**Hour**Time (t)hMetric (derived)60 min ≡ 3,600 seconds.

**Day**Time (t)dMetric (derived)24 hours ≡ 1,440 minutes or 86,400 seconds.

**Year**Time (t)aMetric (derived)365.24 days.

**Hertz**Frequency (f)HzMetric (derived)One cycle per second: 1/s or s

^{−1}

**Angular Frequency**Frequency (f)ωMetricRadians per second. 1 x s

^{-1}≡ 60 x min

^{-1}

**Decibel**SounddBMetricLogarithmic unit to describe a ratio which could be intensity, power, sound pressure, voltage or in common usage loudness.

**Kilogram meters per second**Momentumkg m/sMetricMomentum = Mass x Velocity. The derived unit is newton second.

**Miles per hour**SpeedmphImperialDistance divided by time.

**Meters per second**Speedm/s or kphMetricDistance divided by time.

**Gravity Imperial**

Acceleration of Gravity (g)ft/s

^{2}Imperial1 g = 32.174 ft/s

^{2 }= 386.1 in/s

^{2 }= 22 mph/s.

^{}**Gravity Metric**Acceleration of Gravity (g)m/s

^{2}Metric1 g = 9.81 m/s

^{2}= 35.30394 (km/h)/s.

**Feet per second**Massft/sImperial

**Grams**MassgMetric (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**(from World Metrology Day May 2019): Planck’s constant divided by 6.626,070,15 × 10^{−34}m^{−2}s**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).

**Grain**MassgrImperial / USCS1 Grain = 1⁄7000 lb and ≈ 0.0648 g or 64.8 mg.

**Dram**MassdrImperial / USCS1 Dram = 27 11⁄32 gr and ≈ 1.77 g.

**Ounce**MassozImperial1 Ounce = 1/16 pound or 16 dr ≈ 28.35 g.

**Pound**MasslbImperial / USCS1 Pound = 16 oz ≈ 0.45 kg. The pound is one of the fundamental Imperial units of measurement.

**Hundredweight**MasscwtImperial / 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**MasstonImperial / 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).

**Slug**MassslugUSCS1 slug = 1 lb

_{f}·s

^{2}/ft (A mass that accelerates by 1 ft/s

^{2}when a force of one pound (lb

_{f}) is exerted on it).

**Density**Density (ρ)kg/m

^{3}MetricDensity = mass divided by volume in kilogram per cubic meter (kg/m

^{3}).

**Denier**Linear Densityden or DMetric (derived)Linear density is a measure of the fineness or heaviness of yarn/fiber/fibre used in textiles. Denier is most common used in 🇬🇧

**UK**and 🇺🇸

**US**.

1 denier = 1/9,000,000 kg/m = 1.111 111

^{-7}kg/m. 1 denier = 0.035 ounces/5.6 miles of yarn/fiber/fibre.

For example, denier is still commonly used to describe the thickness/opacity of tights and pantyhose:

- 10 denier or less: ultra sheer
- 10 to 30 denier: sheer
- 30 to 40 denier: semi-opaque
- 40 to 70 denier: opaque
- 70 denier or more” thick opaque.

**Tex**Linear DensitytexMetric (derived)Linear density is a measure of the “fineness” of yarn/fiber/fibre used in textiles. Tex is most commonly used in 🇨🇦

**Canada**and 🇪🇺

**Continental Europe**.

1 tex = 1 gram per kilometer (1g/km) = 0.035 ounces/0.62 miles (0.35oz/0.62m) of yarn/fibre/fiber.

**Decitex**Linear DensitydtexMetric (derived)Linear density is a measure of the “fineness” of yarn/fiber/fibre used in textiles. Decitex is the SI unit for the linear density of fibers/fibres/yarn in kg/m.

1 dtex = 0.0000001 kg/m ≡ 1 gram per 10 kilometers.

**Mommes**WeightmmTraditionalMommes is the traditionally used to measure the weight of silk fabrics. Mommes is just one of many specialized unit of measurements still used in the textile industry. 1 momme = 0.1280019 ounces per square yard (4.340 g/m

^{²}). Heavier silks are more durable, more opaque and appear more “wooly”. Here’s some examples:

- 3-5 mm Gauze (open weave, needlepoint canvases, facings, linings)
- 4-6 mm Organza (bridal wear, evening wear, sheer curtains)
- 5-16 mm Habutai (simple plain weave, used for linings, light clothing, lingerie etc.)
- 6-8 mm Chiffon (translucent, lightweight, used for blouses, scarves, lingerie etc.)
- 12-16 mm Crepe de Chine (crisp, crimpled silk, hundreds of weaves and variations)
- 12-30 mm Charmeuse (weaved so the front has a sheen and the reverse is dull, tends to cling, used for drapes, bridal gowns, ties, linings etc.)
- 35-40 mm Noil/Raw silk (rough texture, dull like cotton, often blended to make other materials. Silk over 30 mm is likely to be opaque).

**Newton**Force, Weight (F)NMetric (derived)Named after Sir Isaac Newton. Kg and m/s

^{2}

**Kilopond**Force (F)kpMetric9.80665 Newtons

**Pond**Force (F)pMetric9,80665 x 10

^{-3}Newtons

**Newton meter**Torque (M)MetricN x m = kg x m

^{2}x s

^{-2}

**Joule**Work, Energy (E)JMetric (derived)N x m = W x s = kg x m

^{2}x s

^{-2}

**Watt**Power, Radiant Flux (P)wMetric (derived)J x s

^{-1}= kg x m

^{2}x s

^{-3}

**Kilowatt**Power (P)kwMetric1 Kilowatt ≡ 1,000 Watts.

**Horsepower**Power (P)hpTraditional1 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.

**Pascal**Pressure, StressPaMetric (derived)One newton per square metre. Named after Blaise Pascal.

**Bar**Power (P)barMetricThe bar is a metric unit of pressure (but not an SI unit). 1 bar= 100,000 Pa (1 bar = 10

^{5}Pa which is slightly less than current average atmospheric pressure on Earth at sea level.

**Pounds per square inch**Pressurepsi or lbf/in

^{2}ImperialPound-force per square inch (lbf/in

^{2}). PSI is a measure of force per unit area. 1 psi ≈ 6894.8 Pascal or 0.0689 Bar.

**Kelvin**Temperature (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.

**Centigrade**Temperature (T)°CMetric (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 / 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.

**Fahrenheit**Temperature (T)°FImperial / USCSA 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)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 × 10^{12}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 metre**Luminance (L)cd/m

^{2}Metric (derived)The intensity of light emitted from a surface per unit area in a given direction.

**Lumen**Luminous 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.

**Lux**Illuminance (E)lxMetric (derived)One lumen per square metre. lm x s = cd x sr x m

^{-2}

**Lumen Seconds**Light quantity (Q)lsMetriclm x s

**Diopter**Refractive Index (D)dptMetric1 x m

^{-1}

**Ampere**Current (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.

**Coulomb**Electric Charge (Q)CMetric (derived)Charge carried by a constant current of one ampere in one second.

**Volt**Voltage, 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 m

^{2}x (s

^{3}x A)

^{-1}

**Ohm**Electrical Resistance, Impedance (R)ΩMetric (derived)W x A

^{-1}= kg x m

^{2}x (s

^{3}x A

^{2})

^{-1 }

(Mnemonic to remember the order of color coding on resistors)

^{}

**Farad**Electrical 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.

**Siemens**Electrical Conductance (S)SMetric (derived)One Siemens is equal to the reciprocal of one ohm. Named after Ernst Werner von Siemens.

**Henry**Electrical 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.

**Weber**Magnetic 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.

**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 DecayBqMetric (derived)Bq = 1 x s

^{-1}

**Mole**Amount 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 ×10^{23}elementary entities.

One of 7 SI base units of measurement.

**Paper Bale**Paper QuantityreamImperial1 ream = 500 sheets of paper.

**Dozen**Quantitiesdz 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.