The most common units that are used in most counties are metric units (SI System) and U.S. customary units. British Imperial units are also still in use in some countries.

**What is Length?**

**Length is defined as “Distance between two points”.**

**What is the standard unit of length?**

There is not a standard unit of length. However, Meter is the base unit of length in metric System and the Yard is the base unit of length in the Imperial and U.S. customary systems.

**What is the base unit of Length in SI Metric System?**

The base unit of length is Meter. Meter is defined as:

"The length of the path travelled by light in a vacuum within 1⁄299792458 seconds" (It is approximately equal to 1.0936 yards).

### Other Units of Length

There are also other units for measuring large and small quantities, the most common are:

kilometer | km | 1,000 m |

hectometer | hm | 100 m |

decameter | dam | 10 m |

meter |
m |
1 m |

decimeter | dm | 0.1 m |

centimeter | cm | 0.01 m |

millimeter | mm | 0.001 m |

We can see that each unit is 10 times larger than the previous unit. We can convert the units to other units by multiplying or dividing with 10 factors.

Following are the metric length units and the respective multiple factors to convert from meters:

Units |
deca | hecto | kilo | mega | giga | tera | peta | exa | zetta | yotta |

Factor |
10^{1} |
10^{2} |
10^{3} |
10^{6} |
10^{9} |
10^{12} |
10^{15} |
10^{18} |
10^{21} |
10^{24} |

Following are the metric length units and the respective submultiple factors to convert from meters:

Unit |
deci | centi | milli | micro | nano | pico | femto | atto | zepto | yocto |

Factor |
10^{–1} |
10^{–2} |
10^{–3} |
10^{–6} |
10^{–9} |
10^{–12} |
10^{–15} |
10^{–18} |
10^{–21} |
10^{–24} |

### What is the base unit of Length in Imperial and U.S. customary systems?

The basic unit of length is the Yard in Imperial and U.S. customary systems. There are other important units commonly used in Non-SI Length Units:

thou |
1⁄1000 of an inch |

line |
1⁄12 of an inch |

inch |
25.4 mm |

foot |
12 inches |