Speed converter
Convert between km/h, mph, m/s, knots, feet per second and Mach, then watch your speed line up against a cheetah, a bullet train and the speed of sound.
That's 1.85× as fast as a galloping horse, while a cheetah is 1.08× faster. In one minute you'd cover 1.036 miles.
What it means
How fast is that?
Reference speeds are typical values. Mach uses the speed of sound in dry air at 20 °C (343 m/s).
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Learn
Three things worth knowing
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The 0.6 rule
To turn km/h into mph in your head, take a bit more than half: 100 km/h is about 62 mph, 50 is about 31. Going the other way, add roughly 60%.
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Where the knot comes from
Sailors threw a weighted log overboard on a rope tied with knots at even spacing and counted how many ran out in 30 seconds. One knot per half-minute became one nautical mile per hour.
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Mach is not a fixed speed
Sound travels slower in cold air, so Mach 1 is about 1,235 km/h near the ground but only about 1,062 km/h at airliner cruising height. A plane can speed up and still fly at the same Mach number.
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Popular speed conversions
Background
About speed units
Speed is distance divided by time. Road signs use km/h almost everywhere, except in the UK and the US, which use mph. Scientists use meters per second, sailors and pilots use knots, and fast aircraft are described in Mach, a multiple of the speed of sound.
Quick mental math: to go from km/h to mph, multiply by about 0.6 (100 km/h ≈ 62 mph). From m/s to km/h, multiply by 3.6.