Millimetre

File:EM Spectrum Properties edit.svg

Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter.

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. 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.

Definition

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>Template:Cite web</ref> A millimetre, Template:Sfrac of a metre, is therefore the distance travelled by light in Template:Sfrac of a second.

Informal terminology

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 symbols

For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has [[CJK Compatibility|Template:Sc form symbols]] for:<ref name=comp>Template:Cite web</ref>

• millimetre - Template:Unichar
• square millimetre - Template:Unichar
• cubic millimetre Template:Unichar

In Japanese typography, these square symbols are used for laying out unit symbols without distorting the grid layout of text characters.

Measurement

On a metric ruler, the smallest measurements are normally millimetres.<ref>Template:Cite 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>Template:Cite 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>Template:Cite 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>Template:Cite web</ref>

See also

• Metric system
• Orders of magnitude (length)
• Submillimetre astronomy