🚀 Speed Converter

Enter a value and pick its unit — every other unit updates instantly below.

Value

Unit

Everything through metres per second

Your figure becomes metres per second, then divides out into the other five units. The factors are exact except for Mach:

1 km/h = 0.277778 m/s   (divide by 3.6)
1 mph  = 0.44704 m/s
1 ft/s = 0.3048 m/s
1 knot = 0.514444 m/s   = 1.852 km/h
Mach 1 = 340.29 m/s     (sea level, 15 °C)

Between the two road units, 1 mph is 1.609344 km/h and 1 km/h is 0.621371 mph. A useful trick for road signs: multiply km/h by 5 and divide by 8, so 80 km/h reads as 50 mph, which is accurate to under 1%.

Road speeds side by side

mph	km/h	m/s
20	32.19	8.94
30	48.28	13.41
40	64.37	17.88
50	80.47	22.35
60	96.56	26.82
70	112.65	31.29

Running and cycling pace is the same conversion upside down. 10 km/h is 2.78 m/s, which is a 6 minute kilometre or a 9:39 mile.

Mach is a ratio to the local speed of sound, and that speed depends on air temperature, not on altitude directly. This tool uses 340.29 m/s, the standard sea level value at 15 °C. At a cruising altitude of -50 °C the speed of sound is nearer 300 m/s, so Mach 0.85 up there is a slower ground speed than the same Mach number down here.

Frequently asked questions

How fast is 100 km/h in mph?

62.14 mph. The reverse, 60 mph, is 96.56 km/h, which is why a 100 km/h limit and a 60 mph limit are treated as the same road.

How fast is 1 knot in mph?

1.15078 mph, or 1.852 km/h exactly. A knot is one nautical mile per hour, and a nautical mile is one minute of latitude, which is what keeps it in use for shipping and aviation.

How fast is Mach 1?

340.29 m/s at sea level in 15 degree air, which is 1,225 km/h or 761 mph. In colder air sound travels more slowly, so Mach 1 at 11,000 m is closer to 1,062 km/h.