About the Speed Converter
This speed converter translates a velocity between miles per hour, kilometres per hour, metres per second, feet per second, knots and Mach number. Pick the unit you have and the one you need; the headline shows that single conversion while the table lists every other unit, and a context line tells you roughly what the speed feels like — walking, highway driving or airliner cruising.
Drivers use it for foreign speed limits, runners and cyclists for pace figures, sailors and pilots for knots, and students for physics problems that need SI units. Because mph, km/h, knots and ft/s are all defined exactly in metres and seconds, those conversions are exact.
Mach is different: it is a ratio to the local speed of sound, which changes with air temperature. This tool uses 343 m/s (dry air at 20 °C, about 767 mph). At the 15 °C standard sea-level atmosphere sound travels at about 340.3 m/s, and at airliner cruising altitudes closer to 295 m/s.
How to use the speed converter
- 1Enter the speed you want to convert.
- 2Choose its current unit, such as mph or knots.
- 3Choose the unit you need.
- 4Read the headline answer, the full unit table and the real-world comparison.
Formula and method
The converter first changes your speed into metres per second, then divides by the size of the target unit in m/s. A mile is exactly 1609.344 m, so 1 mph = 1609.344 ÷ 3600 = 0.44704 m/s. A kilometre per hour is 1000 ÷ 3600 = 1/3.6 m/s, a knot is one nautical mile (1852 m) per hour ≈ 0.514444 m/s, and 1 ft/s is 0.3048 m/s.
Mach number divides the speed by the speed of sound. The tool uses 343 m/s, the value for dry air at 20 °C; because sound slows in colder air, a given ground speed is a higher Mach number at altitude.
- mph
- Miles per hour (1 mph = 0.44704 m/s)
- km/h
- Kilometres per hour (1 km/h = 0.27778 m/s)
- kn
- Knot, one nautical mile per hour (1.852 km/h)
- Mach
- Speed ÷ speed of sound (343 m/s here)
Worked examples
60 mph in km/h
60 × 0.44704 = 26.8224 m/s. Multiplying by 3.6 gives 96.56 km/h, and dividing by 0.3048 gives exactly 88 ft/s — the classic "60 mph is 88 feet per second".
100 km/h speed limit in mph
100 km/h is 27.778 m/s. Dividing by 0.44704 m/s per mph gives 62.14 mph, so a 100 km/h limit is just over 62 mph.
Boat cruising at 30 knots
One knot is 1.852 km/h, so 30 knots is 55.56 km/h. Converting to mph gives about 34.52 mph.
Speed of sound
343 m/s divided by the 343 m/s reference is exactly Mach 1. In road units that is about 767 mph, or 1,235 km/h.
Frequently asked questions
How do I convert mph to km/h?+
Multiply miles per hour by 1.609344. For example, 70 mph × 1.609344 = 112.65 km/h. For a quick mental estimate multiply by 1.6.
How do I convert km/h to m/s?+
Divide km/h by 3.6, because one kilometre per hour is 1000 metres per 3600 seconds. So 90 km/h ÷ 3.6 = 25 m/s.
What is a knot in mph and km/h?+
A knot is one nautical mile (1852 m) per hour, which is exactly 1.852 km/h and about 1.15078 mph. It is used at sea and in aviation.
How fast is Mach 1?+
Mach 1 is the speed of sound, which depends on air temperature. At 20 °C it is about 343 m/s (767 mph); at 15 °C about 340 m/s (761 mph); at 35,000 ft only about 295 m/s (660 mph).
Why is 60 mph equal to 88 feet per second?+
A mile is 5,280 feet and an hour is 3,600 seconds. 60 × 5,280 ÷ 3,600 = 88 exactly, which is why 60 mph is a handy reference for reaction-distance calculations.