Unit |
Symbol | Description |

astronomical unit |
au | Astronomical units are used to measure the huge distances in space. One astronomical unit is approximately 149 597 870 691 meters. |

attometer |
am | Metric system. One Quintillionth of a meter |

cable |
cable | Cable is a unit of length that was used at sea. One cable is about 219 meters. |

centimeter |
cm | centimeter is a unit of length used by the metric system, that is equivalent to 1/100 th of a meter. |

chain |
ch | One chain is 100 links |

decameter |
dam | The decameter is a unit of length of the metric system equivalent to 10 m. It's not commonly used. |

decimeter |
dm | Metric system. One tenth of a meter |

fathom |
fathom | The fathom represents the distance between a man's outstretched fingertips. It's used mainly at sea. |

femtometer |
fm | Metric system. One quadrillionth of a meter |

foot |
ft | The international foot is equal to 12 inches. |

foot (survey) |
ft | The United States survey foot is defined as 1200/3937 meters. |

furlong |
fur | The furlong is a measure of distance in the imperial system. It's equal to 660 feet. |

hand |
hh | Hand is a unit of length used to measure the height of horses. One hand is 4 inches. |

hectometer |
hm | Metric system. 100 meters. |

inch |
in | The international inch, equivalent to 25.40 mm. |

kilometer |
km | A kilometer is another unit of length of the metric system. It's equivalent to 1000 meters. |

league (land) |
leagues | The league was intended to represent the distance a person can walk in an hour. It's no longer used but is often found in literature (eg.20000 Leagues under the sea). |

league (sea) |
leagues | The league was intended to represent the discance a person can walk in an hour. It's no longer used but is often found in leterature (eg.20000 Leagues under the sea). |

li (Chinese) |
li | A unit of length used in China. One li is 500 m. |

light-year |
ly | The light-year is the distance light travels in vacuum in one year. It's equivalent to approximately 9,460,730,472,580.8 km. |

link |
li | Link is a unit of length in the Imperial system. It is equal to 33/50 of a foot. It is rarely used. |

meter |
m | Meter is the basic unit of length in the metric system. The official definition of meter, since 1983 is: the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. |

micrometer |
µm | Metric system. One millionth of a meter |

micron |
µ | Equivalent to micrometer |

mil |
mil | Mil is used in the US in engineering, to specify tolerances. It's equal to 0.001 inch. |

mile |
mi | One international mile is 5280 feet. |

mile (survey) |
mi | One U.S. survey mile is equal to 8000 links |

millimeter |
mm | Metric system. One thousandths of a meter |

nanometer |
nm | Metric system. One billionth of a meter |

nautical mile |
nmi | Nautical mile is a unit of length to specify distance for maritime and aviation purposes. One nautical mile is 1852 meters. |

picometer |
pm | Metric system. One trillionth of a meter |

rod |
rd | One rod is 25 links |

thou |
thou | One thou is the same as 1 mil. and is equal to one thousandths of an inch. |

yard |
yd | The yard is equivalent to 3 feet. |