Centimetre

centimetre
centimetre
	A carpenter's ruler with centimetre divisions
General information
Unit system	SI
Unit of	length
Symbol	cm
Conversions
1 cm in ...	... is equal to ...
millimetres	10 mm
imperial & US system	~0.3937 in

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

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^[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.