Unit of length

Unit of length

A unit of length is a way of measuring length or distance.

Common units of length in the International System of Units (SI) are:
* metre and its multiples, such as "centimetre" or "kilometre"

Non-SI units of length include:
* fermi (fm) (= 1 femtometre in SI units)
* angstrom (Å) (= 100 picometres in SI units)
* micron (= 1 micrometre in SI units)
* Norwegian/Swedish mil (= 10,000 metres)

Common Imperial units and U.S. customary units of length include:
* inch (25.4 mm)
* mil (one thousandth of an inch, one thou)
* foot ( 12 inches, 0.3048 m)
* yard (3 ft, 0.9144 m)
* (terrestrial) mile (5280 ft, 1609.344 m)

In addition, the following are used by mariners:
* fathom (for depth) (1.8288 m)
* nautical mile (1852 m)

Surveyors in the United States continue to use:
* chain (~20.1m)
* rod (also called pole or perch) (~5 m)

Horse racing keeps alive:
* furlong (~201 m)

Astronomical measure uses:
*astronomical unit (AU) (~149 gigametres)
*light year (ly) (~9.46 petametres)
*parsec (pc) (~30.8 petametres), including kiloparsec (kpc) and megaparsec (Mpc)

Physics also uses:
*Planck length
*Bohr radius

Archaic units of distance are described in the article on Ancient weights and measures. They include:
*cana
*cubit
*league
*li (China)
*pace (the "double pace" of about 5 feet used in Ancient Rome)
*verst (Russia)

In everyday conversation, and in informal literature, it is common to see lengths measured in units of objects of which everyone knows the approximate width. Common examples are:
*Football field (generally around 110 metres, depending on the country)
*Widths of a human hair (around 80 micrometres)
*A beard-second is a unit created as a teaching concept. It is the distance that a beard grows in a second (about 5 nanometres)
*Smoot, a jocular unit of length created as part of an MIT fraternity prank.

ee also

*Systems of measurement
*Medieval weights and measures
*English unit
*Orders of magnitude (length)


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