Speed Converter (km/h, mph, m/s, knots, Mach)
Convert a speed between km/h, mph, m/s, knots, feet per second, and Mach. Enter a value, pick the two units, and the result updates as you type. Everything runs in your browser.
How the conversion works
Every unit on this page is defined by how many meters per second it represents. The input is converted to m/s, then from m/s into the target unit:
result = value × (m/s per source unit) ÷ (m/s per target unit)
The metric relationship is worth memorizing because it comes up constantly: 1 m/s = 3.6 km/h exactly, since there are 3600 seconds in an hour and 1000 meters in a kilometer.
Why Mach is only approximate
Mach is not a fixed speed. It is a ratio: the speed of an object divided by the speed of sound in the surrounding air. And the speed of sound is not constant, it depends primarily on air temperature.
At sea level and 15 °C, sound travels at about 340.3 m/s, which is the reference this converter uses. At a typical airliner cruising altitude of 11,000 m, where the air is around −56 °C, sound travels at only about 295 m/s. The same true airspeed therefore corresponds to a noticeably higher Mach number at altitude than at sea level.
This is why aircraft switch from indicated airspeed to Mach number above a certain altitude: what limits the airframe at high altitude is the ratio to the local speed of sound, not the absolute speed. Treat the Mach figures here as sea-level approximations rather than exact values for any specific flight condition.
Quick reference table
| From | km/h | mph | m/s | knots |
|---|---|---|---|---|
| 1 km/h | 1 | 0.62137 | 0.27778 | 0.53996 |
| 1 mph | 1.60934 | 1 | 0.44704 | 0.86898 |
| 1 m/s | 3.6 | 2.23694 | 1 | 1.94384 |
| 1 knot | 1.852 | 1.15078 | 0.51444 | 1 |
| 1 ft/s | 1.09728 | 0.68182 | 0.3048 | 0.59248 |
Common speed limits
| Limit | km/h | mph |
|---|---|---|
| Urban (Europe) | 50 | 31.1 |
| Urban (US) | 48.3 | 30 |
| Rural road | 100 | 62.1 |
| US interstate | 112.7 | 70 |
| Motorway (Europe) | 130 | 80.8 |
Practical examples
Driving abroad
The useful shortcut is that mph is roughly km/h divided by 1.6, or km/h times 0.6. A 70 mph US limit is 113 km/h, and a 130 km/h European motorway limit is 81 mph. For quick checks while driving, remember three anchors: 30 mph ≈ 50 km/h, 60 mph ≈ 100 km/h, and 70 mph ≈ 113 km/h.
Running and cycling pace
Runners usually think in pace (minutes per kilometer or mile) rather than speed. To convert speed to pace, divide 60 by the speed in km/h. Running at 12 km/h gives 60 ÷ 12 = 5 minutes per kilometer. A 4-hour marathon (42.195 km) averages 10.5 km/h, or about 5:41 per kilometer.
Wind speed
Weather reports use km/h in most of Europe, mph in the US and UK, and knots in aviation and marine forecasts. A gale at 60 km/h is 37 mph or 32 knots. Marine and aviation forecasts stay with knots because they pair naturally with nautical miles for navigation calculations.
Physics calculations
Kinetic energy, momentum, and acceleration formulas expect SI units, which means meters per second. Converting km/h to m/s by dividing by 3.6 is therefore the first step in most such calculations. Free fall reaches about 9.81 m/s after one second, which is 35.3 km/h.
Frequently asked questions
How many mph is 100 km/h?
62.14 mph. Conversely, 100 mph is 160.93 km/h.
How do I convert m/s to km/h?
Multiply by 3.6. This is exact, not an approximation: an hour has 3600 seconds and a kilometer has 1000 meters, so the factor is 3600 ÷ 1000.
What is a knot?
One nautical mile per hour, which is 1.852 km/h or 1.151 mph. It is used in maritime and air navigation because a nautical mile corresponds to one minute of latitude, which makes chart calculations straightforward.
How fast is the speed of sound?
About 343 m/s (1235 km/h, 767 mph) in dry air at 20 °C. It rises with temperature and falls in colder air, which is why it is around 295 m/s at airliner cruising altitude.
Why is Mach approximate on this page?
Because the speed of sound varies with air temperature and altitude. This converter uses the standard sea-level value of 340.3 m/s. A precise Mach figure requires knowing the local speed of sound at the specific altitude and temperature.
How do I convert speed to pace for running?
Divide 60 by the speed in km/h to get minutes per kilometer. At 10 km/h, 60 ÷ 10 = 6 minutes per kilometer. For miles, divide 60 by the speed in mph.
Related converters
- Length converter, for the distance component
- Acceleration converter, for rate of change of speed
- All unit converters