Speed converter
Convert between mph, km/h, m/s, knots and ft/s — for driving abroad, running, sailing and physics problems.
Exact conversion factors; results rounded to three decimals.
How this calculator works
Speed is distance divided by time, so unit conversions multiply or divide twice: once for the distance unit and once for the time unit. A kilometre per hour is 1,000 metres per 3,600 seconds, which is 0.2778 m/s — the factor used here. A mile per hour is exactly 0.44704 m/s, and a knot is exactly 1,852 metres per hour, or 0.5144 m/s.
Knots are used in aviation and marine navigation because they relate directly to degrees of latitude: one nautical mile is one minute of latitude. Running pace is often given in minutes per kilometre or per mile, which is a reciprocal relationship — a faster speed means a smaller pace number, so pace conversions cannot be done by simple multiplication. This tool converts speed only; for pace, divide 60 by the speed value in the same unit system.
The formula
Convert to metres per second, then to the target unit:
m/s = value × factor(from)
result = m/s / factor(to)
1 km/h = 0.27778 m/s 1 mph = 0.44704 m/s
1 kn = 0.51444 m/s 1 ft/s = 0.3048 m/sSo 100 km/h = 62.137 mph = 27.778 m/s = 53.996 knots = 91.134 ft/s.
Worked example
Converting 100 Kilometres per hour gives 62.137 mph in miles per hour, 27.778 m/s in metres per second and 53.996 kn in knots.
Common mistakes
- Ignoring the time unit. Distance conversions alone are not enough: mph to km/h multiplies by 1.609, because the hour cancels out.
- Confusing speed and pace. Running pace is minutes per unit, the reciprocal of speed. Converting pace needs 60 ÷ speed, not a unit factor.
- Rounding speed for navigation. In aviation and marine work, small speed errors become large position errors; keep enough decimals.
Frequently asked questions
How fast is 100 km/h in mph?
100 km/h is 62.14 mph. Multiply km/h by 0.621371 to get mph, or mph by 1.609344 to get km/h.
What is a knot in mph?
One knot is 1.15078 mph, or 0.51444 m/s. Knots are nautical miles per hour.
How do I convert running pace to speed?
Divide 60 by the pace in minutes per unit. A 5:00 min/km pace is 12 km/h; a 6:00 pace is 10 km/h.
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