# SI base unit

The **SI base units** are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities: they are notably a basic set from which all other SI units can be derived. The units and their physical quantities are the second for time, the metre (sometimes spelled meter) for length or distance, the kilogram for mass, the ampere for electric current, the kelvin for thermodynamic temperature, the mole for amount of substance, and the candela for luminous intensity. The SI base units are a fundamental part of modern metrology, and thus part of the foundation of modern science and technology.

Symbol | Name | Base quantity |
---|---|---|

s | second | time |

m | metre | length |

kg | kilogram | mass |

A | ampere | electric current |

K | kelvin | thermodynamic temperature |

mol | mole | amount of substance |

cd | candela | luminous intensity |

The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science and technology. ^{[citation needed]}

The names and symbols of SI base units are written in lowercase, except the symbols of those named after a person, which are written with an initial capital letter. For example, the *metre* has the symbol m, but the *kelvin* has symbol K, because it is named after Lord Kelvin and the *ampere* with symbol A is named after André-Marie Ampère.

A number of other units, such as the litre, astronomical unit, and electronvolt, are not formally part of the SI, but are accepted for use with SI.