List of conversion factors
This article gives a list of conversion factors for several physical quantities. A number of different units are shown and expressed in terms of the corresponding SI unit.
Conversions between units in the metric system are defined by their prefixes and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name. Within each table, the units are listed alphabetically, and the SI units are highlighted.
The following quantities are considered: length, area, volume, plane angle, solid angle, mass, density, time, frequency, velocity, volumetric flow rate, acceleration, force, pressure, torque, energy, power, action, dynamic viscosity, kinematic viscosity, electric current, electric charge, electric dipole, electromotive force, electrical resistance, capacitance, magnetic flux, magnetic flux density, inductance, temperature, information entropy, luminous intensity, luminance, luminous flux, illuminance, radiation.
| Symbol | Definition |
| ≡ | exactly equal |
| ≈ | approximately equal to |
| ≘ | corresponds to |
| indicates that digits repeat infinitely | |
| of chiefly historical interest |
Plane angle
Mass
Notes:- See Weight for detail of mass/weight distinction and conversion.
- Avoirdupois is a system of mass based on a pound of 16 ounces, while Troy weight is the system of mass where 12 troy ounces equals one troy pound.
- The symbol is used to denote standard gravity in order to avoid confusion with the g symbol for gram.
| Name of unit | Symbol | Definition | Relation to SI units |
| atomic mass unit, unified | u; AMU | Same as dalton | ≈ |
| atomic unit of mass, electron rest mass | me | ≈ | |
| bag | ≡ 60 kg | = 60 kg | |
| bag | ≡ 94 lb av | = | |
| barge | ≡ short ton | = | |
| carat | kt | ≡ gr | = mg |
| carat | ct | ≡ 200 mg | = 200 mg |
| clove | ≡ 8 lb av | = | |
| crith | ≡ mass of 1 L of hydrogen gas at STP | ≈ 89.9349 mg | |
| dalton | Da | 1/12 the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest | ≈ |
| dram | dr t | ≡ 60 gr | = |
| dram | dr av | ≡ gr | = |
| electronvolt mass-equivalent | eV/c2 | ≡ 1 eV / c2 | = |
| gamma | γ | ≡ 1 μg | = 1 μg |
| grain | gr | ≡ lb av | ≡ |
| grave | gv | grave was the original name of the kilogram | ≡ 1 kg |
| hundredweight | long cwt or cwt | ≡ 112 lb av | = |
| hundredweight ; cental | sh cwt | ≡ 100 lb av | = |
| hyl; metric slug | ≡ 1 kgf / 1 m/s2 | = | |
| kilogram | kg | ≈ mass of the prototype near Paris≈ mass of 1 litre of water | |
| kip | kip | ≡ av | = |
| mark | ≡ 8 oz t | = | |
| mite | ≡ gr | = | |
| mite | ≡ g | = 50 mg | |
| ounce (apothecary; troy) | oz t | ≡ lb t | = |
| ounce | oz av | ≡ lb | = |
| ounce | oz | ≡ 28 g | = 28 g |
| pennyweight | dwt; pwt | ≡ oz t | = |
| point | ≡ ct | = 2 mg | |
| pound (avoirdupois) | lb av | ≡ = grains | ≡ |
| pound (metric) | ≡ 500 g | = 500 g | |
| pound (troy) | lb t | ≡ grains | = |
| quarter | ≡ long cwt = 2 st = 28 lb av | = | |
| quarter | ≡ short ton | = | |
| quarter, long | ≡ long ton | = | |
| quintal | q | ≡ 100 kg | = 100 kg |
| scruple | s ap | ≡ 20 gr | = |
| sheet | ≡ lb av | = 647.9891 mg | |
| slug; geepound | slug | ≡ × 1 lb av × 1 s2/ft | ≈ |
| stone | st | ≡ 14 lb av | = |
| ton, assay | AT | ≡ 1 mg × 1 long ton ÷ 1 oz t | = 32. g |
| ton, assay | AT | ≡ 1 mg × 1 short ton ÷ 1 oz t | = 29.1 g |
| ton, long | long tn or ton | ≡ | = |
| ton, short | sh tn | ≡ | = |
| tonne | t | ≡ | = |
| wey | ≡ 252 lb = 18 st | = | |
| zentner | Ztr. | Definitions vary. |
Speed or velocity
A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.Force
| Name of unit | Symbol | Definition | Relation to SI units |
| atomic unit of force | ≡ | ≈ | |
| dyne | dyn | ≡ g⋅cm/s2 | = 10−5 N |
| kilogram-force; kilopond; grave-force | kgf; kp; gvf | ≡ × 1 kg | = |
| kip; kip-force | kip; kipf; klbf | ≡ × | = |
| milligrave-force, gravet-force | mgvf; gvtf | ≡ × 1 g | = |
| long ton-force | tnf | ≡ × 1 long ton | = |
| newton | N | A force capable of giving a mass of one kilogram an acceleration of one metre per second per second. | = 1 N = 1 kg⋅m/s2 |
| ounce-force | ozf | ≡ × 1 oz | = |
| pound-force | lbf | ≡ × 1 lb | = |
| poundal | pdl | ≡ 1 lb⋅ft/s2 | = |
| short ton-force | tnf | ≡ × 1 short ton | = |
| sthene | sn | ≡ 1 t⋅m/s2 | = 103 N |
Energy
| Name of unit | Symbol | Definition | Relation to SI units |
| barrel of oil equivalent | boe | ≈ | ≈ |
| British thermal unit | BTUISO | ≡ | = |
| British thermal unit | BTUIT | = | |
| British thermal unit | BTUmean | ≈ | |
| British thermal unit | BTUth | ≈ | |
| British thermal unit | BTU39 °F | ≈ | |
| British thermal unit | BTU59 °F | ≡ | = |
| British thermal unit | BTU60 °F | ≈ | |
| British thermal unit | BTU63 °F | ≈ | |
| calorie | calIT | ≡ | = |
| calorie | calmean | of the energy required to warm one gram of air-free water from 0 °C to 100 °C at a pressure of 1 atm | ≈ |
| calorie | calth | ≡ 4.184 J | = |
| Calorie | Cal | ≡ 1 kcal = | = |
| calorie | cal3.98 °C | ≈ | |
| calorie | cal15 °C | ≡ 4.1855 J | = |
| calorie | cal20 °C | ≈ | |
| Celsius heat unit | CHUIT | ≡ 1 BTUIT × 1 K/°R | = |
| cubic centimetre of atmosphere; standard cubic centimetre | cc atm; scc | ≡ 1 atm × 1 cm3 | = |
| cubic foot of atmosphere; standard cubic foot | cu ft atm; scf | ≡ 1 atm × 1 ft3 | = |
| cubic foot of natural gas | ≡ | = | |
| cubic yard of atmosphere; standard cubic yard | cu yd atm; scy | ≡ 1 atm × 1 yd3 | = |
| electronvolt | eV | ≡ e × 1 V | ≡ |
| erg | erg | ≡ 1 g⋅cm2/s2 | = 10−7 J |
| foot-pound force | ft lbf | ≡ × 1 lb × 1 ft | = |
| foot-poundal | ft pdl | ≡ 1 lb⋅ft2/s2 | = |
| gallon-atmosphere | imp gal atm | ≡ 1 atm × 1 gal | = |
| gallon-atmosphere | US gal atm | ≡ 1 atm × 1 gal | = |
| hartree, atomic unit of energy | Eh | ≡ me⋅α2⋅c2 | ≈ |
| horsepower-hour | hp⋅h | ≡ 1 hp × 1 h | = |
| inch-pound force | in lbf | ≡ × 1 lb × 1 in | = |
| joule | J | The work done when a force of one newton moves the point of its application a distance of one metre in the direction of the force. | = 1 J = 1 m⋅N = 1 kg⋅m2/s2 = 1 C⋅V = 1 W⋅s |
| kilocalorie; large calorie | kcal; Cal | ≡ | = |
| kilowatt-hour; Board of Trade Unit | kW⋅h; B.O.T.U. | ≡ 1 kW × 1 h | = |
| litre-atmosphere | l atm; sl | ≡ 1 atm × 1 L | = |
| quad | ≡ 1015 BTUIT | = | |
| rydberg | Ry | ≡ R∞⋅ℎ⋅c | ≈ |
| therm | ≡ | = | |
| therm | ≡ | = | |
| thermie | th | ≡ 1 McalIT | = |
| tonne of coal equivalent | TCE | ≡ 7 Gcalth | = |
| tonne of oil equivalent | toe | ≡ 10 GcalIT | = |
| ton of TNT | tTNT | ≡ 1 Gcalth | = |
| watt-hour | W⋅h | ≡ 1 W × 1 h | = |
| watt-second | W⋅s | ≡ 1 J | = |
Kinematic viscosity
Electromotive force, electric potential difference
Magnetic flux density
Temperature
| Name of unit | Symbol | Definition | Relation to SI units |
| degree Celsius | °C | ≡ − 273.15 | ≡ + 273.15 |
| degree Delisle | °De | = 373.15 − × | |
| degree Fahrenheit | °F | ≡ × + 32 | ≡ × |
| degree Newton | °N | = × + 273.15 | |
| degree Rankine | °R; | ≡ × | ≡ × 5/9 |
| degree Réaumur | °Ré | = × + 273.15 | |
| degree Rømer | °Rø | = × + 273.15 | |
| Regulo Gas Mark | GM | ≡ × 25 + 250 | ≡ × + 394.26 |
| kelvin | K | ≡ change in the thermodynamic temperature that results in a change of thermal energy by 1.380 649 × 10−23 J. |
Information entropy
| Name of unit | Symbol | Definition | Relation to SI units | Relation to bits |
| natural unit of information; nit; nepit | nat | |||
| shannon | Sh | ≡ ln × nat | ≈ | = 1 bit |
| hartley; ban | Hart; ban | ≡ ln × nat | ≈ | |
| bit | bit; b | = 1 bit | ||
| nibble | ≡ 4 bits | = 22 bit | ||
| byte | B | ≡ 8 bits | = 23 bit | |
| kilobyte | kB | ≡ | = bit | |
| kibibyte | KiB | ≡ | = 213 bit = bit |
Modern standards prefer the shannon to the bit as a unit for a quantity of information entropy, whereas the storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning.
Luminous intensity
The candela is the preferred nomenclature for the SI unit.| Name of unit | Symbol | Definition | Relation to SI units |
| candela | cd | The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. | |
| candlepower | cp | ≡ cd The use of candlepower as a unit is discouraged due to its ambiguity. | = 1 cd |
| candlepower | cp | Varies and is poorly reproducible. Approximately 0.981 cd. | ≈ 0.981 cd |
Radiation
Radiation – source activity
Although becquerel and hertz both ultimately refer to the same SI base unit, Hz is used only for periodic phenomena, and Bq is only used for stochastic processes associated with radioactivity.Radiation – exposure
The roentgen is not an SI unit and the NIST strongly discourages its continued use.Radiation – equivalent dose
Although the definitions for sievert and gray would seem to indicate that they measure the same quantities, this is not the case. The effect of receiving a certain dose of radiation is variable and depends on many factors, thus a new unit was needed to denote the biological effectiveness of that dose on the body; this is known as the equivalent dose and is shown in Sv. The general relationship between absorbed dose and equivalent dose can be represented aswhere H is the equivalent dose, D is the absorbed dose, and Q is a dimensionless quality factor. Thus, for any quantity of D measured in Gy, the numerical value for H measured in Sv may be different.