Speed Converter

Convert between km/h, mph, m/s, knots, and ft/s. Includes reference tables for road speed limits, aviation airspeeds, and maritime navigation.

Quick Converter

Result
100 km/h = 62.1371 mph
mph = km/h × 0.621371192237334

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About Speed Units

Speed expresses distance per unit time. In SI terms, speed is measured in meters per second (m/s), but everyday contexts use km/h (most countries), mph (US and UK), knots (aviation and maritime), or Mach (high-speed aerodynamics).

Key exact relationships

  • 1 km/h = 1/3.6 m/s exactly (1000 m / 3600 s)
  • 1 mph = 0.44704 m/s exactly (from the exact mile definition)
  • 1 knot = 1 nautical mile per hour = 1852/3600 m/s exactly (≈ 0.514444 m/s)
  • 1 ft/s = 0.3048 m/s exactly

Where each unit is used

  • m/s — Scientific work, physics, and engineering calculations.
  • km/h — Road speed in Europe, Canada, Australia, Asia, and most of the world.
  • mph — Road speed in the US and UK.
  • Knots — Aviation (airspeed and ground speed) and maritime navigation.
  • Mach — Aerodynamics, where Mach 1 is the local speed of sound.

Note that the speed of sound varies with temperature and altitude, so Mach is not a fixed unit. It is dimensionless and must be converted with a known speed of sound.