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A carpenter's ruler with centimetre divisions
General information
Unit systemSI
Unit oflength
1 cm in ...... is equal to ...
   millimetres   10 mm
   imperial & US system   ~0.3937 in
Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is in-between 1 meter to 1 millimeter.

A centimetre (International spelling) or centimeter (American spelling), with SI symbol cm, is a unit of length in the International System of Units (SI) equal to one hundredth of a metre, centi being the SI prefix for a factor of 1/100.[1] Equivalently, there are 100 centimetres in 1 metre. The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.

Though for many physical quantities, SI prefixes for factors of 103—like milli- and kilo-—are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements; for instance, human height is commonly measured in centimetres.[2][3] A centimetre is approximately the width of the fingernail of an average adult person.

Equivalence to other units of length[edit]

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[edit]

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[4]
  • in the CGS system, the centimetre is used to measure capacitance, where 1 cm of capacitance = 1.113×10−12 farads[5]
  • in maps, centimetres are used to make conversions from map scale to real world scale (kilometres)
  • to represent second moment of areas (cm4)
  • 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[edit]

For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:[6]

  • centimetre – U+339D SQUARE CM
  • square centimetre – U+33A0 SQUARE CM SQUARED
  • cubic centimetre – U+33A4 SQUARE CM CUBED

These characters are each equal in size to one Chinese character and are typically used only with East Asian, fixed-width CJK fonts.

See also[edit]


  1. ^ "Decimal multiples and submultiples of SI units". Bureau International des Poids et Mesures. 2014. Retrieved 5 July 2015.
  2. ^ "Using the BMI-for-Age Growth Charts". cdc.gov. Centers for Disease Control. Archived from the original on 30 January 2014. Retrieved 5 July 2014.
  3. ^ Price, Beth; et al. (2009). MathsWorld Year 8 VELS Edition. Australia: MacMillan. p. 626. ISBN 978-0-7329-9251-4.
  4. ^ "Rain Measurement". www.weathershack.com.
  5. ^ Weisstein, Eric W. "Capacitance -- from Eric Weisstein's World of Physics". scienceworld.wolfram.com.
  6. ^ CJK Compatibility excerpt from The Unicode Standard, Version 10.0.

External links[edit]