length · International · Modern
1 km = 1000 m by the SI prefix kilo-.
Converter
length · International · Modern
metre
mexact
- Record
- M001
- Definition quality
- Standardized
- Conversion mode
- multiplicative
- Calculator
- Fully calculable
None identified for current SI definition; name etymology not researched in this batch.
Definition
SI base unit of length. Its definition fixes the speed of light in vacuum at exactly 299,792,458 m/s, with the second defined from the caesium-133 hyperfine frequency.
Reference value
One metre is equal to 1 metre.
History & use
The metric metre began with a geodetic definition tied to Earth's meridian; it was later embodied by an international prototype bar, then defined by krypton-86 wavelengths, and since 1983 by the speed of light.
Modern use
International SI base unit for length; all SI length units are related to the metre through SI prefixes or derived expressions.
Did you know?
Its definition moved from Earth, to a metal bar, to atomic radiation, and finally to a universal constant.
Sources & evidence
Source tier Tier A · confidence High
- Definition Source — https://www.bipm.org/en/measurement-units/si-defining-constants
- History Source — https://www.nist.gov/nist-museum/defining-international-system-units-si
- Modern Use Source — https://www.bipm.org/en/measurement-units/si-base-units
- Trivia Source — https://www.nist.gov/nist-museum/defining-international-system-units-si
Related measurements
length · International · Modern
1 cm = 0.01 m by the SI prefix centi-.
length · International · Modern
1 mm = 0.001 m by the SI prefix milli-.
inch
inlength · UK / US · Modern / historical
1 international inch = exactly 0.0254 m.
foot
ftlength · UK / US · Modern / historical
1 international foot = exactly 0.3048 m.
yard
ydlength · UK / US · Modern / historical
1 international yard = exactly 0.9144 m.
mile
milength · UK / US · Modern / historical
1 international mile = exactly 1609.344 m = 1760 yd.
length · UK / US · Modern / historical
1 international nautical mile = exactly 1852 m.