Speed Converter
Convert any speed between the five units in common use: kilometers per hour, miles per hour, knots, meters per second, and feet per second. Enter a value, choose the units, and the result updates as you type.
- 100 km/h in mph
- 62.137119 mph
Each unit dominates a different domain. Roads use km/h in most of the world and mph in the US and UK. Aviation and shipping use knots (nautical miles per hour). Science uses m/s, the SI unit. Wind speeds appear in all four depending on the country and context, which is where this converter earns its keep.
How it's calculated
1 mph = 1.609344 km/h · 1 knot = 1.852 km/h · 1 m/s = 3.6 km/h
All conversions pass through meters per second as the base unit. The knot comes from the nautical mile (exactly 1,852 m), one minute of latitude, which is why air and sea navigation still use it.
Worked example
A 70 mph US highway limit is 112.7 km/h. A 15-knot wind is 27.8 km/h or 17.3 mph. Usain Bolt's peak sprint speed of about 12.4 m/s converts to 44.6 km/h or 27.8 mph.
Frequently asked questions
›How do I quickly convert km/h to mph in my head?
Multiply by 0.6: 100 km/h is about 60 mph (exact: 62.1). Going the other way, add 60%: 50 mph is about 80 km/h (exact: 80.5). Both are close enough for road signs.
›What exactly is a knot?
One nautical mile per hour, or 1.852 km/h. The name comes from sailors counting knots in a rope paid out behind the ship to measure speed. Nautical miles match minutes of latitude, which makes them convenient for navigation charts.
›Why does science use meters per second?
It is the SI unit, consistent with meters for distance and seconds for time, so physics formulas work without conversion factors. 1 m/s equals exactly 3.6 km/h.
›What are typical speeds in each unit?
Walking is about 5 km/h (3 mph, 1.4 m/s). A city car drives 50 km/h (31 mph). A commercial jet cruises around 900 km/h (490 knots). A hurricane starts at sustained winds of 64 knots (119 km/h, 74 mph).
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