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ToolBoxGenie

Speed Converter

Converters · Added 9 August 2026

Convert a speed between the units used on road signs, in aviation, at sea and in physics — including knots and Mach.

Result

1 km/h in miles per hour

0.621371192 mph

1 km/h = 0.621371192 mph

The same value in every unit

Metres per second (m/s)
0.277777778
Kilometres per hour (km/h)
1
Miles per hour (mph)
0.621371192
Feet per second (ft/s)
0.911344415
Knot (kn)
0.539956803
Mach (sea level) (Ma)
0.000816297211

Mach is quoted at sea level in the standard atmosphere (15 °C), where the speed of sound is 340.29 m/s. It falls as air gets colder, so Mach 1 at altitude is slower.

How to use the speed converter

  1. 1Enter the speed in the Value box.
  2. 2Pick the unit it is given in and the unit you want it in.
  3. 3The result appears with the conversion factor spelled out, and every other unit is listed below it.
  4. 4Use Swap units to reverse the conversion instantly.

Examples

A motorway speed limit

Input
100 km/h
Result
62.1371192 mph

The common European 100 km/h limit is a little over 62 mph; the UK's 70 mph limit is about 113 km/h.

Sprint speed in physics units

Input
36 km/h
Result
10 m/s

Dividing km/h by 3.6 gives m/s exactly — the cleanest conversion in this tool.

Cruising airliner

Input
0.85 Mach
Result
289.2465 m/s (1,041.29 km/h)

Mach here is quoted at sea level. Higher up the air is colder and the speed of sound drops, so the same Mach number is a lower true airspeed.

About the speed converter

Why so many units for one quantity

Speed has more competing units in daily use than almost any other quantity, because different industries standardised at different times and none of them wanted to retrain. Road transport uses km/h or mph depending on the country. Shipping and aviation use knots. Physics and engineering use metres per second, since it composes cleanly with other SI units.

None of these is more correct than the others; they are just anchored to different reference distances and different time bases. The conversions are all exact, apart from Mach, which genuinely varies with conditions.

The mph and km/h relationship worth knowing

A mile is roughly 1.6 kilometres, so a speed in mph is about 1.6 times the same figure in km/h. In practice, a few landmark pairs cover most needs: 30 mph is 48 km/h, 60 mph is 97 km/h, and 100 km/h is 62 mph.

Speed limits are set in round numbers in whichever system the country uses, which is why converted limits always look untidy. A 50 km/h urban limit is 31 mph; a 30 mph limit is 48 km/h. Neither converts to a round number in the other system, and that is expected rather than an error.

Frequently asked questions

How do I convert km/h to m/s in my head?
Divide by 3.6. There are 1,000 metres in a kilometre and 3,600 seconds in an hour, so the factor is exactly 1000/3600. Going the other way, multiply m/s by 3.6.
What exactly is a knot?
One nautical mile per hour, or 1.852 km/h exactly. Because a nautical mile equals one minute of latitude, a speed in knots translates directly into progress across a chart, which is why ships and aircraft kept the unit long after everything else went metric.
Is Mach 1 a fixed speed?
No, and this catches people out. Mach is a ratio to the local speed of sound, which depends on air temperature. At sea level in standard conditions that is 340.29 m/s, the figure used here. At airliner cruising altitude the air is far colder and the figure drops to roughly 295 m/s — so Mach 1 up there is about 160 km/h slower than Mach 1 at ground level.
How do I convert a running pace instead of a speed?
Pace is the inverse of speed — minutes per kilometre rather than kilometres per hour — so it cannot be converted with the same factors. Convert your speed to km/h first, then divide 60 by that number to get minutes per kilometre. At 12 km/h, that is 60 ÷ 12 = 5 minutes per km.

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