SI base units
| Quantity | Unit | Symbol |
|---|---|---|
| Length | metre | 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 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 |
| 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 |
Notes
* 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.
Non-SI units accepted for use with the 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° = (π/180) rad |
| minute* | ′ | 1′ = (1/60)° = (π/10 800) rad | |
| second* | ″ | 1″ = (1/60)′ = (π/648 000) rad | |
| revolution, turn† | r | 1 r = 2π rad | |
| Area | hectare | ha | 1 ha = 1 hm2 = 104 m2 |
| Volume | litre‡ | L, l | 1 L = 1 dm3 = 10-3 m3 |
| Mass | tonne, “metric ton”§ | t | 1 t = 1 Mg = 103 kg |
Notes
* Decimal degrees should be used for division of degrees, except for fields such as astronomy and cartography. The symbols for minute and second are prime and double prime (not single and double quotation marks), respectively.
† Technically, a revolution is a semantic annotation and not a unit. It is included here as it is commonly used for rotational speed.
‡ The symbol “L” is preferred for use in the US, Canada, and Australia.
§ The terms tonne and “metric ton” are restricted to commercial usage; the SI equivalent is the megagram. The term “metric ton” is preferred for use in the US.
Units in use temporarily with the SI
| Name | Symbol | Value in SI units |
|---|---|---|
| nautical mile | nmi | 1 nmi = 1852 m |
| knot | kn | 1 nmi/h = (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 |
Notes
* 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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