When to use it
Use this converter to switch between kilometers per hour, miles per hour, meters per second, knots, feet per second and Mach. It is helpful when driving abroad, reading a car or bike spec sheet, checking wind speeds for sailing or flying, or answering physics questions in meters per second.
How to use it
- Enter the speed in Value.
- Choose the unit you have, such as Kilometers per hour (km/h).
- Choose the unit you want, such as Miles per hour (mph).
- Read the result, or click Copy result.
- Use the swap button to convert back.
The All conversions table shows the same speed in all six units at once.
Worked example
You are driving in France and the motorway limit is 130 km/h. Enter 130, choose km/h and mph, and you get about 80.8 mph. On a smaller road, a 100 km/h limit is 62.14 mph.
The other way round, a US highway limit of 70 mph is about 112.7 km/h.
For physics homework, 100 km/h is 27.78 m/s, shown in the table. That number is useful when working out stopping distances, which use meters and seconds.
Where each unit is used
- km/h: road signs and car speedometers in most of the world.
- mph: roads in the US and UK.
- m/s: science, engineering and weather data.
- Knots: sailing, aviation and marine weather forecasts.
- Mach: aircraft and rockets.
Speed, distance and time
The three are linked: speed = distance ÷ time. If a train covers 300 km in 2 hours, its average speed is 150 km/h, or about 93 mph. Work out the speed in whichever units your numbers use, then convert the answer here.
Tips
- Learn one anchor. 100 km/h ≈ 62 mph is easy to remember and makes quick checks simple.
- Turn m/s into km/h by multiplying by 3.6. It is the quickest mental shortcut between the two.
- Read wind forecasts carefully. Some give wind in knots, others in km/h or mph.
- Use feet per second for sports. Coaches sometimes quote sprint and ball speeds this way.
Common mistakes
- Mixing up mph and km/h on rental cars. Many cars show both scales on the speedometer, with one in smaller numbers.
- Treating knots as mph. A 20-knot wind is 23 mph, a noticeable difference.
- Assuming Mach is a fixed speed. It depends on air temperature and altitude.