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:
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Since an inch is officially defined as exactly 25.4 millimetres, 1 millimetre is precisely <templatestyles src="Fraction/styles.css" />5⁄127 inches (≈ 0.03937 inches).
Definition
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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".[1]
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[2]
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.[3]
- Precision engineering rulers may show increments of 0.5 mm.
- Digital calipers often measure to 0.01 mm accuracy.[4]
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).[5] - The smallest visible object to the human eye is around 0.02–0.04 mm (e.g., a thin human hair).[6] - A typical sheet of paper is between 0.07 mm and 0.18 mm thick; copy paper is about 0.1 mm.[7]
See also
References
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