# Units: SI Prefixes for Powers of Ten

Info by Interest | 12/06/2013 at 00:58

Within the International System of Units, some prefixes for decimal powers are defined, which I would like to list in this info. This prefixes are also called SI-prefixes, where SI is an abbreviation for the French term "Système international d’unités" (International System of Units).

In this table, all prefixes are quoted together with their abbreviation (symbol column) and their conversion factor:

Prefix | Symbol | Power | Factor |

Yotta | Y | 10^24 | 1 000 000 000 000 000 000 000 000 |

Zetta | Z | 10^21 | 1 000 000 000 000 000 000 000 |

Exa | E | 10^18 | 1 000 000 000 000 000 000 |

Peta | P | 10^15 | 1 000 000 000 000 000 |

Tera | T | 10^12 | 1 000 000 000 000 |

Giga | G | 10^9 | 1 000 000 000 |

Mega | M | 10^6 | 1 000 000 |

Kilo | k | 10^3 | 1000 |

Hecto | h | 10^2 | 100 |

Deca | D | 10^1 | 10 |

- | - | 10^0 | 1 |

Deci | d | 10^-1 | 0.1 |

Centi | c | 10^-2 | 0.01 |

Milli | m | 10^-3 | 0.001 |

Micro | µ | 10^-6 | 0.000 001 |

Nano | n | 10^-9 | 0.000 000 001 |

Pico | p | 10^-12 | 0.000 000 000 001 |

Femto | f | 10^-15 | 0.000 000 000 000 001 |

Atto | a | 10^-18 | 0.000 000 000 000 000 001 |

Zepto | z | 10^-21 | 0.000 000 000 000 000 000 001 |

Yocto | y | 10^-24 | 0.000 000 000 000 000 000 000 001 |

These prefixes are used primarily for physical metric units such as meter or gram by simply prepending the prefix to the base unit (for example, decimeter or kilogram). Since numbers become cumbersome and confusing long in very large or very small scales, it is a good idea to do not write the numbers in their full length and to write an abbreviation instead.

On the one hand, this abbreviation can be made by specifying the powers that are also listed in the table (for example 3.28*10^24 meters) and on the other hand, it can be made by using these SI-prefixes (for example 3.28 meters). Otherwise, you have to write a number with 24 digits which is barely graspable nor readable.

But also in normal language use and in everyday life, the prefixes are often used. For instance, we can think about millimeters (0.001 meters), centimeters (0.01 meters), gigabyte (1 billion byte), kilograms (1000 grams) or millisecond (0.001 seconds).

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