Everyday measurement units are often defined as fractions or multiples of other units. Fractions or multiple of SI units are named using a prefix and the name of the base unit. All prefixes are based on powers of 10. For example, a length of 1000 meters is also called a kilometer because the prefix *kilo* means “one thousand,” which in scientific notation is 10^{3} (1 kilometer = 1000 m = 10^{3} m). The prefixes used and the powers to which 10 are raised are listed in the table below.

Prefix | Symbol | Factor | Example |
---|---|---|---|

femto | f | 10^{−15} | 1 femtosecond (fs) = 1 × 10^{−15} s (0.000000000000001 s) |

pico | p | 10^{−12} | 1 picometer (pm) = 1 × 10^{−12} m (0.000000000001 m) |

nano | n | 10^{−9} | 4 nanograms (ng) = 4 × 10^{−9} g (0.000000004 g) |

micro | µ | 10^{−6} | 1 microliter (μL) = 1 × 10^{−6} L (0.000001 L) |

milli | m | 10^{−3} | 2 millimoles (mmol) = 2 × 10^{−3} mol (0.002 mol) |

centi | c | 10^{−2} | 7 centimeters (cm) = 7 × 10^{−2} m (0.07 m) |

deci | d | 10^{−1} | 1 deciliter (dL) = 1 × 10^{−1} L (0.1 L ) |

kilo | k | 10^{3} | 1 kilometer (km) = 1 × 10^{3} m (1 000 m) |

mega | M | 10^{6} | 3 megahertz (MHz) = 3 × 10^{6} Hz (3 000 000 Hz) |

giga | G | 10^{9} | 8 gigayears (Gyr) = 8 × 10^{9} yr(8 000 000 000 yr) |

tera | T | 10^{12} | 5 terawatts (TW) = 5 × 10^{12} W (5 000 000 000 000 W) |