Speed is distance over time, so every unit for it is a distance unit divided by a time unit. That makes conversion mechanical, and it also explains why the choice of unit is really a statement about the context: kilometres per hour for road travel almost everywhere, miles per hour in the United States and the United Kingdom, metres per second in physics and engineering, knots in aviation and maritime navigation, feet per second in ballistics, fluid dynamics and aviation climb rates.
The two that cause the most confusion are the nautical ones. A knot is one nautical mile per hour, and a nautical mile was defined as one minute of latitude — which is why it is the natural unit for navigation, since a vessel travelling at one knot covers one minute of latitude per hour.
The tool reduces the input to metres per second once, then multiplies back out into all five units and reports each to two decimal places.
| Unit | To metres per second | Definition status |
|---|---|---|
| km/h | divide by 3.6 | exact |
| mph | multiply by 0.44704 | exact (1 mile = 1609.344 m) |
| m/s | unchanged | base unit |
| knots | multiply by 1.852 ÷ 3.6 | exact (1 knot = 1.852 km/h by definition) |
| ft/s | multiply by 0.3048 | exact |
All five constants are defined exactly by international agreement, and the page carries none of them truncated. The knot is the one that invites a decimal: its factor works out to 0.5144444… recurring, so the code derives it as 1.852 ÷ 3.6 rather than storing the recurring digits. The result is exact at every magnitude, so a million knots converts to precisely 1,852,000 km/h.
The default, 100 km/h. Divided by 3.6 this is 27.7778 m/s. Reported back, the page shows 100.00 km/h, 62.14 mph, 27.78 m/s, 54.00 knots and 91.13 ft/s. The knot figure is very slightly under 54 in exact arithmetic, because a knot is 1.852 km/h and 100 ÷ 1.852 = 53.9957; it rounds to 54.00 on screen.
60 mph, the classic case. Multiplying by 0.44704 gives 26.8224 m/s, which is 96.56 km/h, 52.14 knots and exactly 88.00 ft/s. That last figure is not a coincidence to be memorised so much as a unit identity: a mile is 5,280 feet and an hour is 3,600 seconds, so 5,280 ÷ 60 = 88. It is the conversion constant every driving instructor in the United States knows without knowing why.
One knot. Entering a single knot returns 1.85 km/h, 1.15 mph, 0.51 m/s and 1.69 ft/s. Those ungainly numbers are the reason a sailor works in knots rather than converting.
Because the nautical mile is tied to latitude, so a speed in knots translates directly into degrees and minutes of position on a chart. That relationship disappears if you work in kilometres.
Divide 60 by the minutes per kilometre. A pace of 6:00 per kilometre is 60 ÷ 6 = 10 km/h; a pace of 4:30, which is 4.5 minutes, is 60 ÷ 4.5 = 13.33 km/h. Then use this page if you need the answer in another unit.
About fifteen per cent. A nautical mile is 1,852 metres and a statute mile is 1,609.344, so one knot is 1.15078 mph. The two are close enough to confuse and different enough to matter over a long voyage.
Metres per second, because it is coherent with the SI system: multiplying by seconds gives metres directly, with no conversion factor. Kilometres per hour is a convenience for road traffic and an irritation in equations.
Only relative to whatever you are measuring against. The ground, the aircraft carrying you and the solar system all give different answers, which is why speed is always implicitly a relative measurement.