Millimetre#Measurement
{{short description|Unit of length 1/1000 of a metre}}
{{Infobox unit
| bgcolor =
| name = millimetre
| image = Ruler with millimeter and centimeter marks.png
| caption = Ruler with millimetre and centimetre marks
| standard = SI
| quantity = Length
| symbol = mm
| namedafter = The metric prefix mille (Latin for "one thousand") and the metre
| units1 = micrometres
| inunits1 = {{val|1|e=3|ul=μm}} = 1000 μm
| units2 = centimetres
| inunits2 = {{val|1|e=-1|}} cm = 0.1 cm
| units3 = metres
| inunits3 = {{val|1|e=-3|}} m = 0.001 m
| units4 = kilometres
| inunits4 = {{val|1|e=-6|ul=km}}
| units5 = inches
| inunits5 = {{convert|1|mm|in|disp=out|lk=on|sigfig=5|comma=gaps}}
| units6 = feet
| inunits6 = {{convert|1|mm|ft|disp=out|lk=on|sigfig=5|comma=gaps}}
}}
file:EM Spectrum Properties edit.svg, measured by the metre and its derived scales. The microwave is between 1 metre to 1 millimetre.]]
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 {{val|1000}} micrometres or {{val|1,000,000}} nanometres.
Since an inch is officially defined as exactly 25.4 millimetres, a millimetre is equal to exactly {{frac|5|127}} (≈ 0.03937) of an inch.
Definition
{{further|Metre}}
Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of {{sfrac|{{val|299,792,458}}}} of a second".{{cite web |url=http://www.bipm.org/en/CGPM/db/17/1/ |title=17th General Conference on Weights and Measures (1983), Resolution 1. |access-date=3 December 2013 |publisher=International Bureau of Weights and Measures}} A millimetre, {{sfrac|1000}} of a metre, is therefore the distance travelled by light in {{sfrac|{{val|299,792,458,000}}}} 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 CJK compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has CJK Compatibility#Block for:{{cite web |url=https://www.unicode.org/charts/PDF/U3300.pdf |title=CJK Compatibility |publisher=unicode.org |access-date=3 December 2013}}
- millimetre{{snd}}{{unichar|339C|SQUARE MM}}
- square millimetre{{snd}}{{unichar|339F|SQUARE MM SQUARED}}
- cubic millimetre{{snd}}{{unichar|33A3|SQUARE MM CUBED}}
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.{{cite web |url=http://www.onlineconversion.com/faq_05.htm |title=How do I read a ruler? |publisher=onlineconversion.com |access-date=3 December 2013}} 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.{{cite web |url=http://www.tresnainstrument.com/accuracy_of_calipers.html |title=Accuracy of Calipers |publisher=TresnaInstrument.com |access-date=3 December 2013}}
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.{{cite book |url=https://books.google.com/books?id=kCmyPdxme1AC&pg=PP15 |title=Millimeter Wave Communication Systems |isbn=9781118102756 |last1=Huang |first1=Kao-Cheng |last2=Wang |first2=Zhaocheng |year=2011|publisher=John Wiley & Sons }}
The smallest dimension the human eye can resolve is around 0.02 to 0.04 mm, approximately the width of a thin human hair.{{cite web |url=http://sciencefocus.com/qa/how-small-can-naked-eye-see |title=How Small Can the Naked Eye See? |publisher=Focus Magazine |access-date=3 December 2013}} 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.{{cite web
| url=https://hypertextbook.com/facts/2001/JuliaSherlis.shtml
| title=Thickness of a piece of paper
| first=Juliya
| last=Sherlis
| year=2001
| website=The Physics Factbook
| editor-last=Elert
| editor-first=Glenn
| accessdate=2022-01-21
}}
See also
{{Wiktionary|millimetre}}