# Basic Units and Prefixes for ICSE/ISC Board Exam

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**Units of measurement**

**Base units**

The International System of Units (System International d ‘Unites’ ) is founded on seven base quantities, which are assumed to be mutually independent. These base units are:

Base quantity | SI hast unit | Symbol for unit |

Length | Metre | |

Mass | Kilogram | |

Time | Second | |

Electric Current | Ampere | |

Temperature | Kelvin | |

Amount of substance | Mole | |

Luminous intensity | Candela |

**Prefixes**

Prefixes are used to form decimal multiples and submultiples of Si units. The common prefixes are:

Factor | Prefix | Symbol |

tera | T | |

giga | G | |

mega | M | |

kilo | k | |

hecto | h | |

deka | da | |

pico | p | |

nano | n | |

micro | μ | |

milli | m | |

centi | c | |

deci | d |

The symbol for a prefix is combined with the unit symbol to which it is attached to form a new unit symbol, e. g. kilometer (km) , milligram (mg) , microsecond (μs) .