Speed Converter
km/h, mph, knots and m/s.
Convert
Result
0.6213711922 mph
1 kilometre per hour in mile per hour
1 km/h = 0.6213711922 mph
Speed Conversion Math Formula
A speed is a ratio, distance divided by time, so a speed unit has one unit on top and another underneath. Converting one means converting both parts. Dimensional analysis handles it: chain a fraction for the distance unit and a fraction for the time unit, and each one cancels what it should.
Take km/h to m/s. 1 km = 1,000 m goes on top and 1 h = 3,600 s goes underneath, so km/h × (1,000 ÷ 3,600) = km/h ÷ 3.6. The 3.6 you may remember from school is nothing more than 3,600 ÷ 1,000. The converter passes through metres per second.
The formula
value in B = value in A × (m/s per A) ÷ (m/s per B)km/h to m/s: divide by 3.6. m/s to km/h: multiply by 3.6mph to m/s: multiply by 0.44704
Worked example 1: 100 km/h, in mph
100 km/h × (1,000 m ÷ 1 km) × (1 h ÷ 3,600 s) = 27.7778 m/s27.7778 m/s × (1 mph ÷ 0.44704 m/s)Answer: 62.1371 mph
Distance cancels once and time cancels once, in each step. It is a handy figure to remember for road signs: 100 km/h is about 62 mph.
Worked example 2: 60 mph, in m/s
60 mph × (0.44704 m/s ÷ 1 mph)Answer: 26.8224 m/s
The 0.44704 comes from 1,609.344 m ÷ 3,600 s. One mile per hour is exactly that many metres per second.
Worked example 3: 20 knots, in km/h
1 kn = 1 nautical mile per hour = 1.852 km/h20 kn × (1.852 km/h ÷ 1 kn)Answer: 37.04 km/h
Saying "knots per hour" is a classic error. A knot already means nautical miles per hour.
Worked example 4: A 100 m sprint in 9.58 s, as an average speed in km/h
100 m ÷ 9.58 s = 10.4384 m/s10.4384 m/s × 3.6Answer: 37.5783 km/h
That is the average over the whole race. Over its fastest stretch an elite sprinter runs well above 40 km/h.
Common mistakes to avoid
- Dividing by 3.6 when you should multiply. To turn km/h into m/s you divide by 3.6, and to turn m/s into km/h you multiply. A quick sense check: m/s numbers are the smaller ones. 10 m/s is already 36 km/h.
- Converting only half of the unit. Going from mph to km/h means multiplying by 1.609, which is right because the time unit (the hour) is the same on both sides. Going from mph to m/s needs a second factor for the time unit as well. Always check what sits underneath.
- Mixing nautical and statute miles. One knot is 1.15078 mph, not 1 mph. A boat doing 20 knots is doing about 23 mph.
About speed units
Speed tells you how fast something covers distance. The SI unit is the metre per second, the one used in physics. Road speeds use km/h in most of the world and mph in the US, the UK and a few other places. Sailors and pilots use knots, and ballistics and some engineering use feet per second.
Every factor here is exact. A mile per hour is 1,609.344 m ÷ 3,600 s = 0.44704 m/s, a kilometre per hour is 1 ÷ 3.6 m/s, and a knot is 1,852 m ÷ 3,600 s = 0.514444 m/s.
- Metre per second (m/s)The SI unit of speed. 1 m/s = 3.6 km/h = 2.23694 mph.
- Kilometre per hour (km/h)1 km/h = 0.2777777778 m/s1,000 m in 3,600 s. Used on road signs in most countries.
- Mile per hour (mph)1 mph = 0.44704 m/sUsed on road signs in the US and the UK. Exactly 1.609344 km/h.
- Knot (kn)1 kn = 0.5144444444 m/sOne nautical mile per hour, or 1.852 km/h. Used at sea and in aviation.
- Foot per second (ft/s)1 ft/s = 0.3048 m/sExactly 0.3048 m/s. Used in US engineering and ballistics.
Speed conversion table
| Value | m/s | km/h | mph | kn |
|---|---|---|---|---|
| 1 m/s | 1 | 3.6 | 2.23694 | 1.94384 |
| 1 km/h | 0.277778 | 1 | 0.621371 | 0.539957 |
| 1 mph | 0.44704 | 1.60934 | 1 | 0.868976 |
| 1 kn | 0.514444 | 1.852 | 1.15078 | 1 |
| 1 ft/s | 0.3048 | 1.09728 | 0.681818 | 0.592484 |
Speed converter FAQ
How do I convert km/h to mph?
Multiply by 0.621371, or divide by 1.609344. 90 km/h × 0.621371 = 55.9 mph. A rough rule is to multiply by 0.6, which gives 54 mph, close enough for a road sign.
How do I convert mph to km/h?
Multiply by 1.609344. 70 mph × 1.609344 = 112.65 km/h. A quick estimate is to multiply by 1.6, which gives 112.
How do I convert m/s to km/h?
Multiply by 3.6. 25 m/s × 3.6 = 90 km/h. For the reverse, divide by 3.6.
What is a knot?
One nautical mile per hour: 1.852 km/h, or about 1.1508 mph. A ship doing 15 knots covers 15 nautical miles in an hour, which is 27.78 km.
How fast is the speed of sound?
At 20 °C in dry air it is about 343 m/s, which is 1,235 km/h or 767 mph. It changes with air temperature, so Mach 1 is not one fixed speed.
How do I find speed from distance and time?
Divide distance by time, then convert. A car that covers 150 km in 2 hours averages 75 km/h, which is 20.83 m/s or 46.6 mph.