# Centimetre

A **centimetre** (international spelling as used by the International Bureau of Weights and Measures; symbol **cm**) or **centimeter** (American spelling) is a unit of length in the metric system, equal to one hundredth of a metre, *centi* being the SI prefix for a factor of 1/100.[1] The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.

Centimetre | |
---|---|

A carpenter's ruler with centimetre divisions | |

General information | |

Unit system | metric |

Unit of | length |

Symbol | cm |

Conversions | |

1 cm in ... | ... is equal to ... |

SI units | 10 mm |

imperial & US system | ~0.3937 in |

Look up in Wiktionary, the free dictionary.centimetre |

Though for many physical quantities, SI prefixes for factors of 10^{3}—like *milli-* and *kilo-*—are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements. A centimetre is approximately the width of the fingernail of an average adult person.

## Equivalence to other units of length

1 centimetre = 10 millimetres = 0.01 metres = 0.393700787401574803149606299212598425196850 inches (There are *exactly*2.54 centimetres in one inch.)

One millilitre is defined as one cubic centimetre, under the SI system of units.

## Other uses

In addition to its use in the measurement of length, the centimetre is used:

- sometimes, to report the level of rainfall as measured by a rain gauge [2]
- in the CGS system, the centimetre is used to measure capacitance, where 1 cm of capacitance = 1.113×10
^{−12}farads[3] - in maps, centimetres are used to make conversions from map scale to real world scale (kilometres)
- to represent second moment of areas (cm
^{4}) - as the inverse of the kayser, a CGS unit, and thus a non-SI metric unit of wavenumber: 1 kayser = 1 wave per centimetre; or, more generally, (wavenumber in kaysers) = 1/(wavelength in centimetres). The SI unit of wavenumber is the inverse metre, m
^{−1}.

## Unicode symbols

For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:[4]

- centimetre (㎝) – code 339D
- square centimetre (㎠) – code 33A0
- cubic centimetre (㎤) – code 33A4

They are mostly used only with East Asian fixed-width CJK fonts, because they are equal in size to one Chinese character.

## See also

- 1 E-2 m
- Conversion of units, for comparison with other units of length
- Reciprocal centimetre
- Orders of magnitude (length)

## References

- "Decimal multiples and submultiples of SI units". Bureau International des Poids et Mesures. 2014. Retrieved 5 July 2015.
- Rain Measurement, Rain Gauge, Wireless Rain Gauge, Rain Gage, Rain Gauge Data
- Capacitance - from Eric Weisstein's World of Physics
- CJK Compatibility excerpt from The Unicode Standard, Version 10.0.