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Speed Converter online

Convert between mph, km/h, m/s, knots, mach and more

Speed Converter logo
by
CHUNKY
MUNSTER

How to Use the Speed Converter

  1. Type a speed into any of the six unit fields.
  2. All other fields update live with the equivalent value.
  3. Switch to any other field to see the conversion in reverse.
  4. Mach is calculated against the standard sea-level value (343 m/s).

Speed comes in too many units for any one industry to standardise: cars use mph or km/h, aircraft use knots and Mach above the sound barrier, ships use knots, athletics uses m/s, and physics texts use whatever is convenient. This converter shows the same speed in all six units simultaneously, so you can read off whichever one you need without juggling conversion factors.

How the Speed Converter Works

The conversions use exact international definitions: 1 mile = 1.609344 km, 1 nautical mile = 1.852 km, 1 ft = 0.3048 m. Mach uses the standard sea-level speed of sound (343 m/s); at cruising altitude the actual ratio is slightly higher because cold air has a lower speed of sound.

Frequently Asked Questions

What's a knot, exactly?

One nautical mile per hour. The international nautical mile is exactly 1,852 metres (defined to follow one minute of latitude), so 1 knot = 1.852 km/h ≈ 1.151 mph. Aviation and maritime navigation both use it.

Is the Mach number constant?

No — it's the ratio of speed to the local speed of sound, which depends on temperature. The calculator uses the standard sea-level value of 343 m/s (≈ 1,235 km/h or 767 mph). At cruising altitude where it's colder, the speed of sound is lower, so the same true airspeed gives a higher Mach number.

Why are mph and km/h not exact reciprocals?

Because the conversion factor is irrational in both directions: 1 mile = 1.609344 km exactly, so 60 mph = 96.5606 km/h, not a round number. Most countries' road signs use rounded equivalents (50 mph ≈ 80 km/h) for display.

What's the highest speed this handles?

There's no upper cap — the calculator will happily convert relativistic speeds, but the answer is meaningless because at those speeds Newtonian addition of velocities breaks down. For physics work above ~10% of c, use a relativistic calculator.

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