Speed Converter
Free speed converter: km/h to mph, m/s to km/h, knots and Mach at sea level. Exact definitions, an all-units table and a clear note about Mach being approximate.
How to use Speed Converter
- 1Enter a speed, for example 60 or 120.5.
- 2Choose the From unit and the To unit, such as mph to km/h, or press Swap.
- 3Read the result and the factor line, or open All units to see the speed in every unit.
What makes it better
- km/h, mph, m/s, knots, ft/s, Mach and c in one place
- Exact: 1 mph = 0.44704 m/s and 1 knot = 1.852 km/h
- Mach clearly marked as a sea-level, 15 °C approximation
- Convert and All units modes with the factor displayed
About Speed Converter
Speed Converter changes a speed between kilometres per hour, miles per hour, metres per second, knots, feet per second, Mach and the speed of light. Everything except Mach uses exact definitions, so 5 mph is exactly 8.04672 km/h. Mach depends on air temperature and altitude, so it is given as the approximate sea-level, 15 °C value of 340.29 m/s.
Common uses
- Convert a speed limit between km/h and mph when driving abroad.
- Turn a wind forecast in knots or m/s into km/h.
- Check a sprinter or cyclist's average speed given in m/s against km/h.
- Get a feel for supersonic speeds by seeing Mach 2 in km/h.
Example
Input
5
Result
5 mph = 8.04672 km/h
Good to know
- Mach 1 is the local speed of sound. It is about 340.29 m/s (1,225 km/h) at sea level and 15 °C but lower at altitude, where air is colder, so treat Mach results as approximations.
- The speed of light entry is the exact vacuum value of 299,792,458 m/s.
- Speeds convert exactly, but average speeds over a route should be computed from distance and time, not by converting units.
Speed Converter FAQ
How do I convert km/h to mph?
Multiply km/h by 0.621371 (or divide by 1.609344). So 100 km/h is about 62.137 mph. Set From to km/h and To to mph; the page marks the answer as rounded because the exact value has a long tail.
How many km/h is one m/s?
One metre per second is exactly 3.6 km/h, because there are 3,600 seconds in an hour and 1,000 metres in a kilometre. To go back, divide km/h by 3.6.
How fast is a knot?
A knot is one nautical mile per hour, exactly 1.852 km/h or about 1.15078 mph. Ships, aircraft and shipping forecasts use knots because a nautical mile matches one minute of latitude.
How fast is Mach 1?
About 1,225 km/h (761 mph) at sea level and 15 °C, which is the 340.29 m/s used here. Mach 1 is lower at high altitude, around 295 m/s, so a plane at Mach 1 at cruising height flies slower than the sea-level figure.