SI base units | |||
---|---|---|---|
quantity | name | symbol | definition |
length | meter | m | length of the path travelled by light in vacuum during a time interval of 1/299 792 458 second. |
mass | kilogram | kg | mass of Pt-Ir international standard kept at Sevres, France |
time | second | s | duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. |
electric current | ampere | A | the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in vacuum would produce between these conductors a force equal to 2 × 10-7 newton per meter of length. |
thermodynamic temperature | kelvin | K | the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. |
amount of substance | mole | mol | the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12. |
luminous intensity | candela | cd | the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. |
plane angle | radian | rad | the plane angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius |
solid angle | steradian | sr | solid angle that, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere. |
Prefixes used with SI units | ||||||
---|---|---|---|---|---|---|
Factor | Prefix | Symbol | Factor | Prefix | Symbol | |
101 | deca | da | 10-1 | deci | d | |
102 | hecto | h | 10-2 | centi | c | |
103 | kilo | k | 10-3 | milli | m | |
106 | mega | M | 10-6 | micro | µ | |
109 | giga | G | 10-9 | nano | n | |
1012 | tera | T | 10-12 | pico | p | |
1015 | peta | P | 10-15 | femto | f | |
1018 | exa | E | 10-18 | atto | a | |
1021 | zetta | Z | 10-21 | zepto | z | |
1024 | yotta | Y | 10-24 | yocto | y |
Volume | liter milliliter | L mL | 10-3 10-6 |
Length | angstrom inch | A in. | 10-10m 0.0254m |
Mass | pound | lb. | 0.45359237 kg |
SI derived units | |||
---|---|---|---|
quantity | name | symbol | definition |
frequency | hertz | Hz | 1 / s |
force | newton | N | m kg / s² |
pressure | pascal | Pa | N / m² |
energy | joule | J | N m |
power | watt | W | J / s |
electric charge | coulomb | C | A s |
electric potential | volt | V | W / A |
capacitance | farad | F | C / V |
resistance | ohm | captial greek letter Omega | V / A |
conductance | siemens | S | A / V |
magnetic flux | weber | Wb | V s |
magnetic flux density | tesla | T | Wb / m² |
inductance | henry | H | Wb / A |
luminous flux | lumen | lm | cd sr |
illuminance | lux | lx | lm / m² |