SI base units:
| Quantity | Unit | Symbol |
|---|---|---|
| length | meter | m |
| mass | kilogram | kg |
| time | second | s |
| electric current | ampere | A |
| thermodynamic temperature | kelvin | K |
| amount of substance | mole | mol |
| luminous intensity | candela | cd |
SI prefixes:
| Prefix | Symbol | Multiplication factor | |
|---|---|---|---|
| yotta | Y | 1024 | |
| zetta | Z | 1021 | |
| exa | E | 1018 | |
| peta | P | 1015 | |
| tera | T | 1012 | |
| giga | G | 1 000 000 000 | 109 |
| mega | M | 1 000 000 | 106 |
| kilo | k | 1000 | 103 |
| hecto | h | 100 | 102 |
| deka | da | 10 | 101 |
| deci | d | 0.1 | 10-1 |
| centi | c | 0.01 | 10-2 |
| milli | m | 0.001 | 10-3 |
| micro | µ | 0.000 001 | 10-6 |
| nano | n | 0.000 000 001 | 10-9 |
| pico | p | 10-12 | |
| femto | f | 10-15 | |
| atto | a | 10-18 | |
| zepto | z | 10-21 | |
| yocto | y | 10-24 | |
SI derived units with special names and symbols:
| Quantity | Name | Symbol | Expression in terms of other SI units |
|---|---|---|---|
| angle, plane | radian* | rad | m/m = 1 |
| angle, solid | steradian* | sr | m2/m2 = 1 |
| Celsius temperature | degree Celsius | °C | K |
| electric capacitance | farad | F | C/V |
| electric charge, quantity of electricity | coulomb | C | A·s |
| electric conductance | siemens | S | A/V |
| electric inductance | henry | H | Wb/A |
| electric potential difference, electromotive force | volt | V | W/A |
| electric resistance | ohm | Ω | V/A |
| energy, work, quantity of heat | joule | J | N·m |
| force | newton | N | kg·m/s2 |
| frequency (of a periodic phenomenon) | hertz | Hz | 1/s |
| illuminance | lux | lx | lm/m2 |
| luminous flux | lumen | lm | cd·sr |
| magnetic flux | weber | Wb | V·s |
| magnetic flux density | tesla | T | Wb/m2 |
| power, radiant flux | watt | W | J/s |
| pressure, stress | pascal | Pa | N/m2 |
| activity (referred to a radionuclide) | becquerel | Bq | 1/s |
| absorbed dose, specific energy imparted, kerma | gray | Gy | J/kg |
| dose equivalent, ambient dose equivalent, directional dose equivalent, personal dose equivalent, organ dose equivalent | sievert | Sv | J/kg |
| catalytic activity | katal | kat | mol/s |
* The radian and steradian, previously classified as supplementary units, are dimensionless derived units that may be used or omitted in expressing the values of physical quantities.
Units in Use with SI:
| Quantity | Unit | Symbol | Value in SI units |
|---|---|---|---|
| time | minute | min | 1 min = 60 s |
| hour | h | 1 h = 60 min = 3600 s | |
| day | d | 1 d = 24 h = 86 400 s | |
| week, month, etc. | |||
| plane angle | degree* | ° | 1° = (pi/180) rad |
| minute* | ‘ | 1′ = (1/60)° = pi/10 800) rad | |
| second* | “ | 1″ = (1/60)’ = (pi/648 000) rad | |
| revolution, turn | r | 1 r = 2 pi rad | |
| area | hectare | ha | 1 ha = 1 hm2 = 104 m2 |
| volume | liter** | L, l | 1 L = 1 dm3 = 10-3 m3 |
| mass | metric ton or tonne*** | t | 1 t = 103 kg |
* Decimal degrees should be used for division of degrees, except for fields such as astronomy and cartography.
** The symbol L is preferred for use in the U.S.
*** The terms “metric ton” or “tonne” are restricted to commercial usage.
Units in Use Temporarily with SI:
| Name | Symbol | Value in SI Units |
|---|---|---|
| nautical mile | 1 nautical mile = 1852 m | |
| knot | 1 nautical mile per hour = (1852/3600) m/s | |
| bar* | bar | 1 bar = 100 kPa |
| barn | b | 1 b = 100 fm2 = 10-28 m2 |
| curie | Ci | 1 Ci = 3.7 x 1010 Bq |
| roentgen | R | 1 R = 2.58 x 10-4 C/kg |
| rad | rad, rd** | 1 rad = 10 mGy = 10-2 Gy |
| rem | rem | 1 rem = 10 mSv = 10-2 Sv |
* Use is limited to meteorology.
** When there is risk of confusion with the symbol for radian, rd may be used as the symbol for rad.
The above information has been compiled from various International System of Units (SI) reference publications.
For addition help see a selection of Metric posters, diagrams, and charts.
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Updated: 2013-06-17