How to convert speeds
- Enter the value.
- Pick the From and To units: kilometers per hour, miles per hour, meters per second, knots or feet per second.
- Read the result, the exact factor both ways and a table of the same speed in every unit.
How it works
Each unit is stored as an exact number of meters per second.
| Unit | Exact size in m/s |
|---|---|
| kilometer per hour | 1 ÷ 3.6 = 0.27778 |
| mile per hour | 0.44704 |
| knot | 1,852 ÷ 3,600 = 0.51444 |
| foot per second | 0.3048 |
The mile per hour is exact because 1,609.344 m ÷ 3,600 s = 0.44704 m/s. All results come from multiplying by the “from” size and dividing by the “to” size.
Worked example
A car is driven at 65 mph on a US highway. What is that in km/h, m/s and knots?
- Kilometers per hour: 65 × 1.609344 = 104.61 km/h.
- Meters per second: 65 × 0.44704 = 29.06 m/s.
- Knots: 29.06 ÷ 0.51444 = 56.49 kn.
Stopping distance grows with the square of speed, so the same car at 104.6 km/h needs far more road than at 52 km/h.
Rules of thumb
- Add 60 percent to mph to get km/h (65 mph is about 104 km/h).
- Multiply km/h by 0.62 to get mph.
- Divide m/s by 0.28, or multiply by 3.6, to get km/h.
- A knot is about 1.85 km/h.
Where each unit is used
Road signs use km/h in most countries and mph in the US, UK and a few others. Meteorologists often report wind in m/s or knots. Pilots and sailors use knots. Athletes’ speeds appear in m/s on track timing sheets.
Popular pairs
Open mph to km/h or km/h to mph for ready tables. For distances, see the length converter, and for file sizes and network speeds, the data size converter.
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