Template:Short description Template:Infobox unit
The millimetre (international spelling; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the International System of Units (SI), equal to one thousandth of a metre, which is the SI base unit of length. Therefore, there are one thousand millimetres in a metre, and there are ten millimetres in a centimetre.
One millimetre is equal to Template:Val micrometres or Template:Val nanometres. Since an inch is officially defined as exactly 25.4 millimetres, a millimetre is equal to exactly Template:Frac (≈ 0.03937) of an inch.
DefinitionEdit
Template:Further Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of Template:Sfrac of a second".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A millimetre, Template:Sfrac of a metre, is therefore the distance travelled by light in Template:Sfrac of a second.
Informal terminologyEdit
A common shortening of millimetre in spoken English is "mil". This can cause confusion in the United States, where "mil" traditionally means a thousandth of an inch.
Unicode symbolsEdit
For the purposes of CJK compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has [[CJK Compatibility#Block|Template:Sc form symbols]] for:<ref name=comp>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
- millimetreTemplate:SndTemplate:Unichar
- square millimetreTemplate:SndTemplate:Unichar
- cubic millimetreTemplate:SndTemplate:Unichar
In Japanese typography, these square symbols are used for laying out unit symbols without distorting the grid layout of text characters.
MeasurementEdit
On a metric ruler, the smallest measurements are normally millimetres.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> High-quality engineering rulers may be graduated in increments of 0.5 mm. Digital callipers are commonly capable of reading increments as small as 0.01 mm.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Microwaves with a frequency of 300 GHz have a wavelength of 1 mm. Using frequencies between 30 GHz and 300 GHz for data transmission, in contrast to the 300 MHz to 3 GHz normally used in mobile devices, has the potential to allow data transfer rates of 10 gigabits per second.<ref>Template:Cite book</ref>
The smallest dimension the human eye can resolve is around 0.02 to 0.04 mm, approximately the width of a thin human hair.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A sheet of paper is typically between 0.07 mm and 0.18 mm thick, with ordinary printer paper or copy paper approximately 0.1 mm thick.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>