Millimetre
Template:Short description Template:Infobox unit
The millimetre (SI symbol: mm; international spelling) or millimeter (American spelling) is a unit of length in the International System of Units (SI), equal to one thousandth of a metre, the SI base unit of length.
- 1 metre = 1000 millimetres - 1 centimetre = 10 millimetres
One millimetre is also equal to: - Template:Val micrometres - Template:Val nanometres
Since an inch is officially defined as exactly 25.4 millimetres, 1 millimetre is precisely Template:Frac inches (≈ 0.03937 inches).
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, being Template:Sfrac of a metre, is the distance light travels in Template:Sfrac of a second.
Informal terminology
The term "mil" is sometimes used colloquially for millimetre. However, in the United States, "mil" traditionally means a thousandth of an inch, which may cause confusion.
Unicode symbols
To support layout compatibility with East Asian scripts (CJK), Unicode includes square symbols for:
- Millimetre – Template:Unichar
- Square millimetre – Template:Unichar
- Cubic millimetre – Template:Unichar<ref name=comp>Template:Cite web</ref>
These symbols are often used in Japanese typography to align unit symbols with text characters.
Measurement
- On a standard metric ruler, the smallest divisions are typically millimetres.<ref>Template:Cite web</ref> - Precision engineering rulers may show increments of 0.5 mm. - Digital calipers often measure to 0.01 mm accuracy.<ref>Template:Cite web</ref>
Examples: - Microwaves with a frequency of 300 GHz have a wavelength of 1 mm. - Using frequencies from 30–300 GHz for millimetre-wave communications allows high-speed data transfer (e.g., 10 Gbps).<ref>Template:Cite book</ref> - The smallest visible object to the human eye is around 0.02–0.04 mm (e.g., a thin human hair).<ref>Template:Cite web</ref> - A typical sheet of paper is between 0.07 mm and 0.18 mm thick; copy paper is about 0.1 mm.<ref>Template:Cite web</ref>