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 (or "meter" in US English) 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)

Common Imperial units and U.S. customary units of length include:

• inch (25.4mm)
• foot (0.3048m)
• yard (0.9144m)
• (terrestrial) mile (~1640m)

In addition, the following are used by mariners...

• fathom (for depth) (1.8288m)
• nautical mile (1852m)

...and surveyors in the United States continue to use...

• chain (~20.1m)
• pole, also called rod or perch (~5m)

...while horse racing keeps alive:

• furlong (~201m)

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)

See also

• Ancient weights and measures
• Medieval weights and measures