# Length

The straight line distance between two points.

- The SI unit of length is the metre and is equal to 1650763.73 wavelengths in vacuum of the radiation corresponding to the transition 2p
_{10}-5d_{s}of a krypton 86 atom.

*Conversions*1 foot = 0.3048 m 1 fathom = 1.8288 m 1 mile = 1609 m 1 nautical mile = 1852 m 1 cable = 219.456 m 1 inch = 0.0254 m

*Examples*Classical electron radius 2.817940285x10 ^{-15}mWavelength of red visible light 7x10 ^{-7}mEquatorial radius of the Earth 6.37814x10 ^{6}mOrbital semi-major axis about the sun 1.495979x10 ^{11}m

**The SI unit of Length**

**See also: **Approximate Length, Foot, Mensuration, Metre, Micrometre, Nautical Mile, Pace, SI Units, Surveyor′s Wheel.

**Subjects: ** Physics