Speed Converter
Road signs use miles per hour in the US and UK but kilometres per hour almost everywhere else; sailors and pilots use knots; scientists and sports analysts use metres per second. Switching between them is a daily problem for travellers, drivers hiring cars abroad, cyclists, runners comparing pace to speed, and anyone reading a weather report’s wind speeds. This converter uses exact definitions and shows the factor, so you can double-check by hand.
How to use the speed converter
- Enter the speed.
- Select the unit you have and the unit you need.
- Read the result, the factor and the other common speed units shown below.
Formula
Every speed is converted through metres per second. Result = value × (m/s per “from” unit) ÷ (m/s per “to” unit). Exact definitions: 1 mph = 0.44704 m/s (so 1 mph = 1.609344 km/h), 1 km/h = 1/3.6 m/s, 1 knot = 1 nautical mile per hour = 1.852 km/h and 1 ft/s = 0.3048 m/s.
Worked examples
A US highway limit abroad
A 65 mph limit is 104.61 km/h.
A European motorway in mph
A 120 km/h limit is 74.565 mph.
Wind speed in knots
A 25-knot wind is 28.77 mph, or 46.3 km/h.
Common speed conversions
| Conversion | Result |
|---|---|
| 30 mph | 48.2803 km/h |
| 50 mph | 80.4672 km/h |
| 70 mph | 112.654 km/h |
| 100 km/h | 62.1371 mph |
| 10 m/s | 36 km/h |
| 10 kn | 18.52 km/h |
Pace vs speed
Runners often think in pace (minutes per mile or km) rather than speed. To convert, divide 60 by the pace in minutes: a 6:00 min/km pace is 10 km/h. For travel-time questions use the speed, distance and time calculator. See also the unit converter hub.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- A 55 mph speed limit is how many km/h?
Show answer
55 mph in km/h: 88.51392
- Convert 100 km/h to mph.
Show answer
100 km/h in mph: 62.13711922
Common mistakes to avoid
- Using 1.6 as the mph→km/h factor for long distances; the real figure is 1.609344, and the rounding adds up.
- Treating a knot as a unit of distance — it is already per hour (“knots per hour” is redundant).
- Mixing up km/h and m/s: 1 m/s is 3.6 km/h, so a sprinter at 10 m/s is going 36 km/h.
Frequently asked questions
How do I convert mph to km/h?
Multiply by 1.609344. For 50 mph: 50 × 1.609344 = 80.47 km/h.
How do I convert km/h to mph?
Divide by 1.609344 (or multiply by 0.621371). 100 km/h is 62.14 mph.
How fast is a knot?
One knot is 1.852 km/h, about 1.15078 mph — one nautical mile per hour.
How do I convert m/s to km/h?
Multiply by 3.6. A speed of 20 m/s is 72 km/h.
Why do boats and planes use knots?
A nautical mile is tied to one minute of latitude, which makes navigation on charts straightforward.
Sources and further reading
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.