Speed Converter

How it works

Every speed unit is defined as some number of metres per second. The calculator multiplies your value by the size of the unit it is in to get metres per second, then divides by the size of the unit you want. Because both steps use exact definitions, the result is as precise as the definitions themselves.

The miles-per-hour figure is exact: since 1959 the international mile has been 1,609.344 m, so 1 mph is 1,609.344 ÷ 3,600 = 0.44704 m/s exactly. A knot is one international nautical mile (1,852 m, exactly) per hour, and a kilometre per hour is 1,000 ÷ 3,600 m/s.

The conversion factor is what one unit of the 'from' unit is worth in the 'to' unit, so you can apply it to other values by hand. The table lists the same speed in every unit the converter knows, so a quick comparison across units needs no further clicks.

Formula

metres per second = value × (size of the from unit in m/s)
converted         = metres per second ÷ (size of the to unit in m/s)
factor            = size of from unit ÷ size of to unit

1 m/s = 1          1 km/h = 1000/3600      1 mph = 0.44704
1 ft/s = 0.3048    1 ft/min = 0.3048/60    1 knot = 1852/3600

Example

60 mph, the default, is 60 × 0.44704 = 26.8224 m/s, which is 26.8224 ÷ (1000/3600) = 96.56064 km/h. The factor from mph to km/h is 1.609344, the number of kilometres in a mile.

The table shows the same 60 mph as 88 ft/s, 5,280 ft/min and 52.138575 knots. Going the other way, 100 km/h is 62.137119 mph and 20 knots is 23.015589 mph.

Assumptions and limitations

• US customary and imperial lengths use the 1959 international yard: 1 ft = 0.3048 m and 1 mi = 1,609.344 m exactly, so mph and ft/s factors are exact.
• A knot is the international nautical mile of 1,852 m per hour (adopted 1929; used by the US since 1954 and the UK since 1970). Older UK Admiralty knots (6,080 ft) are about 0.06% larger.
• Mach number is not offered: it depends on the local speed of sound, which varies with temperature and altitude, so it is not a fixed multiple of m/s.
• Results are shown to six decimal places; very small values may display as 0 even though the conversion is computed in full precision.
• A negative speed is rejected. Convert the magnitude and keep track of direction separately.

Frequently asked questions