# SI System **Namespace:** `mp_units::si` **Module:** `mp_units.systems` **Header:** `` **Secondary Headers:** - `` - `` - `` - `` - `` - `` ## Units | Unit Name | Symbol | unit_symbol | Definition | |-----------|:------:|:-----------:|------------| | ampere | A | `A` | kind: [isq::electric_current](isq.md#electric_current) | | becquerel | Bq | `Bq` | [one](core.md#one) / [second](#second)
kind: [isq::activity](isq.md#activity) | | candela | cd | `cd` | kind: [isq::luminous_intensity](isq.md#luminous_intensity) | | coulomb | C | `C` | [ampere](#ampere) * [second](#second) | | degree_Celsius | ℃ (\`C) | `deg_C` | [kelvin](#kelvin)
origin: [zeroth_degree_Celsius](#zeroth_degree_Celsius) | | farad | F | `F` | [coulomb](#coulomb) / [volt](#volt) | | gram | g | `g` | kind: [isq::mass](isq.md#mass) | | gray | Gy | `Gy` | [joule](#joule) / [kilogram](#kilogram)
kind: [isq::absorbed_dose](isq.md#absorbed_dose) | | henry | H | `H` | [weber](#weber) / [ampere](#ampere) | | hertz | Hz | `Hz` | [one](core.md#one) / [second](#second)
kind: [isq::frequency](isq.md#frequency) | | joule | J | `J` | [newton](#newton) * [metre](#metre) | | katal | kat | `kat` | [mole](#mole) / [second](#second) | | kelvin | K | `K` | kind: [isq::thermodynamic_temperature](isq.md#thermodynamic_temperature)
origin: [zeroth_kelvin](#zeroth_kelvin) | | kilogram | — | `kg` | [kilo](#kilo)<[gram](#gram)> | | lumen | lm | `lm` | [candela](#candela) * [steradian](#steradian) | | lux | lx | `lx` | [lumen](#lumen) / square([metre](#metre)) | | magnetic_constant | μ₀ (u_0) | — | mag<4> * mag_power<10, -7> * [π](core.md#π) * [henry](#henry) / [metre](#metre) | | metre | m | `m` | kind: [isq::length](isq.md#length) | | mole | mol | `mol` | kind: [isq::amount_of_substance](isq.md#amount_of_substance) | | newton | N | `N` | [kilogram](#kilogram) * [metre](#metre) / square([second](#second)) | | ohm | Ω (ohm) | `Ω`, `ohm` | [volt](#volt) / [ampere](#ampere) | | pascal | Pa | `Pa` | [newton](#newton) / square([metre](#metre)) | | radian | rad | `rad` | [metre](#metre) / [metre](#metre)
kind: [isq::angular_measure](isq.md#angular_measure) | | second | s | `s` | kind: [isq::duration](isq.md#duration) | | si2019::avogadro_constant | N_A | — | mag_ratio<602'214'076, 100'000'000> * mag_power<10, 23> / [mole](#mole) | | si2019::boltzmann_constant | k | — | mag_ratio<1'380'649, 1'000'000> * mag_power<10, -23> * [joule](#joule) / [kelvin](#kelvin) | | si2019::elementary_charge | e | — | mag_ratio<1'602'176'634, 1'000'000'000> * mag_power<10, -19> * [coulomb](#coulomb) | | si2019::hyperfine_structure_transition_frequency_of_cs | Δν_Cs (dv_Cs) | — | mag<9'192'631'770> * [hertz](#hertz) | | si2019::luminous_efficacy | K_cd | — | mag<683> * [lumen](#lumen) / [watt](#watt) | | si2019::planck_constant | h | — | mag_ratio<662'607'015, 100'000'000> * mag_power<10, -34> * [joule](#joule) * [second](#second) | | si2019::speed_of_light_in_vacuum | c | — | mag<299'792'458> * [metre](#metre) / [second](#second) | | siemens | S | `S` | [one](core.md#one) / [ohm](#ohm) | | sievert | Sv | `Sv` | [joule](#joule) / [kilogram](#kilogram)
kind: [isq::dose_equivalent](isq.md#dose_equivalent) | | standard_gravity | g₀ (g_0) | — | mag_ratio<980'665, 100'000> * [metre](#metre) / square([second](#second)) | | steradian | sr | `sr` | square([metre](#metre)) / square([metre](#metre))
kind: [isq::solid_angular_measure](isq.md#solid_angular_measure) | | tesla | T | `T` | [weber](#weber) / square([metre](#metre)) | | volt | V | `V` | [watt](#watt) / [ampere](#ampere) | | watt | W | `W` | [joule](#joule) / [second](#second) | | weber | Wb | `Wb` | [volt](#volt) * [second](#second) | !!! note "Inline Namespaces" The `mp_units::si::si2019` namespace is inline in `mp_units::si`, making its units directly accessible from the parent namespace. ## Non-SI units accepted for use with the SI | Unit Name | Symbol | unit_symbol | Definition | |-----------|:------:|:-----------:|------------| | arcminute | ′ (') | `arcmin` | mag_ratio<1, 60> * [degree](#degree) | | arcsecond | ″ ('') | `arcsec` | mag_ratio<1, 60> * [arcminute](#arcminute) | | are | a | `a` | square([deca](#deca)<[metre](si.md#metre)>) | | astronomical_unit | au | `au` | mag<149'597'870'700> * [metre](si.md#metre) | | dalton | Da | `Da` | mag_ratio<16'605'390'666'050, 10'000'000'000'000> * mag_power<10, -27> * [kilogram](si.md#kilogram) | | day | d | `d` | mag<24> * [hour](#hour) | | degree | ° (deg) | `deg` | mag_ratio<1, 180> * [π](core.md#π) * [radian](si.md#radian) | | electronvolt | eV | `eV` | mag_ratio<1'602'176'634, 1'000'000'000> * mag_power<10, -19> * [joule](si.md#joule) | | hectare | — | `ha` | [hecto](#hecto)<[are](#are)> | | hour | h | `h` | mag<60> * [minute](#minute) | | litre | L | `l`, `L` | cubic([deci](#deci)<[metre](si.md#metre)>) | | minute | min | `min` | mag<60> * [second](si.md#second) | | tonne | t | `t` | mag<1000> * [kilogram](si.md#kilogram) | !!! note "Namespace" These units are defined in the `mp_units::non_si` namespace and are made available in the `mp_units::si` namespace through a using-directive. ## Prefixes | Name | Symbol | Definition | |------|:------:|------------| | `quecto` | q | `mag_power<10, -30>` | | `ronto` | r | `mag_power<10, -27>` | | `yocto` | y | `mag_power<10, -24>` | | `zepto` | z | `mag_power<10, -21>` | | `atto` | a | `mag_power<10, -18>` | | `femto` | f | `mag_power<10, -15>` | | `pico` | p | `mag_power<10, -12>` | | `nano` | n | `mag_power<10, -9>` | | `micro` | µ (u) | `mag_power<10, -6>` | | `milli` | m | `mag_power<10, -3>` | | `centi` | c | `mag_power<10, -2>` | | `deci` | d | `mag_power<10, -1>` | | `deca` | da | `mag_power<10, 1>` | | `hecto` | h | `mag_power<10, 2>` | | `kilo` | k | `mag_power<10, 3>` | | `mega` | M | `mag_power<10, 6>` | | `giga` | G | `mag_power<10, 9>` | | `tera` | T | `mag_power<10, 12>` | | `peta` | P | `mag_power<10, 15>` | | `exa` | E | `mag_power<10, 18>` | | `zetta` | Z | `mag_power<10, 21>` | | `yotta` | Y | `mag_power<10, 24>` | | `ronna` | R | `mag_power<10, 27>` | | `quetta` | Q | `mag_power<10, 30>` | ## Point Origins | Name | Type | Definition | |------|:----:|------------| | `absolute_zero` | absolute | [isq::thermodynamic_temperature](isq.md#thermodynamic_temperature) | | `chrono_point_origin` | absolute | [isq::time](isq.md#time) | | `ice_point` | relative | ::mp_units::point<[milli](#milli)<[kelvin](#kelvin)>>(273'150) | | `zeroth_degree_Celsius` | — | alias to [ice_point](#ice_point) | | `zeroth_kelvin` | — | alias to [absolute_zero](#absolute_zero) |