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Meter (m)

Quantity: Length · Category: SI base

The meter is the SI base unit of length. Since 1983 it has been defined by the speed of light: the distance light travels in vacuum in exactly 1/299,792,458 of a second. This ties the meter to a constant of nature rather than any physical object.

Relation to SI

Base unit — defined via c = 299,792,458 m/s exactly

Examples

  • A standard doorway is about 2 meters tall.
  • Light travels about 300 million meters every second.