When to use this converter
Use it for speed limits abroad, a treadmill or running pace, wind speeds in a forecast, or boat and aircraft speeds given in knots.
Where the numbers come from
Each speed unit is a length divided by a time, so it inherits exact definitions: a mile per hour is 1,609.344 meters in 3,600 seconds, exactly 0.44704 m/s. A knot is one nautical mile (1,852 m) per hour, and a kilometer per hour is 1,000 m in 3,600 s.
Quick mental math
To go from mph to km/h, multiply by about 1.6; from km/h to mph, multiply by about 0.62. A knot is roughly 1.15 mph. Use the converter when you need the exact figure. Planning a drive? The fuel cost calculator estimates the gas bill, and the length converter turns kilometers into miles.
Worked examples
Driving: a 65 mph limit is about 104.6 km/h, and a 130 km/h European motorway limit is about 80.8 mph. Canadian and Mexican signs are in km/h, so 100 km/h means roughly 62 mph. The mph to km/h and km/h to mph pages list common limits.
Running and cycling: a treadmill at 6 mph is a 10-minute mile, or about 9.66 km/h. A cyclist averaging 25 km/h is riding at about 15.5 mph. To turn a speed into a pace, divide 60 by the speed in mph for minutes per mile.
Wind and boats: a 20-knot wind is about 23 mph or 37 km/h, and hurricane force starts at 64 knots, about 74 mph. See knots to mph. Meters per second appear in science and in some weather data: multiply by 3.6 for km/h.
Units and rounding: speedometers and GPS apps round to whole numbers, and a car speedometer is usually set to read slightly high. Converting a displayed 100 km/h gives 62.14 mph, but the true speed may be a little lower. For physics problems, convert to meters per second first, since formulas such as kinetic energy (½mv²) expect SI units: 1 mph is exactly 0.44704 m/s.
Running pace works the other way: 5 minutes per kilometer is 12 km/h, or about 7.46 mph.