Meter (m)
Definition
The meter (symbol m) is the base unit of length in the International System of Units (SI). It measures linear distance and is defined by fixing the numerical value of the speed of light in vacuum at exactly 299,792,458 metres per second.
History
The meter originated in the French Revolution as one ten-millionth of the distance from the equator to the North Pole along the Paris meridian. The first prototype platinum bar, the mètre des Archives, was deposited in 1799.
In 1889 the General Conference on Weights and Measures adopted a platinum–iridium prototype bar held at the BIPM near Paris. Successive redefinitions tied the meter first to the wavelength of krypton-86 radiation in 1960, then in 1983 to the distance light travels in 1/299,792,458 of a second. The 2019 SI revision retained that definition while making it derivable directly from the fixed numerical value of the speed of light.
Standard reference
Defined by the BIPM SI Brochure (9th edition, 2019) by fixing the speed of light at 299,792,458 m/s exactly. The U.S. usage is governed by NIST Special Publication 811.
Common conversions
| 1 m | = 100 cm |
|---|---|
| = 1,000 mm | |
| = 3.28084 ft | |
| = 39.3701 in |