How do I convert km/h to mph?
Type a value in either box, and the answer shows it in the other unit as you type.
- Miles per hour (mph)
- 0.621371
1 km/h = 0.621371 mph.
Miles per hour (mph): 0.621371. 1 km/h = 0.621371 mph.
Miles per hour (mph) by kilometers per hour (km/h)
How to calculate
Converts kilometers per hour (km/h) to miles per hour (mph) and back, with the exact unit definitions.
Example with the default inputs (Kilometers per hour (km/h) 1): 1 km/h = 0.621371 mph.
Formula: mph = km/h × 0.621371192237 (the same as km/h ÷ 1.609344)
- 1 kilometer per hour = 0.621371192237 miles per hour, from the exact definitions in NIST SP 811.
- Exact on the typed decimals: at most 6 decimal places (6 significant digits below 0.0001), rounded half up; an answer of 1 billion or more shows at most 15 significant digits.
Worked examples
Each example is checked against the calculator on every build.
- Kilometers per hour (km/h) 1 gives Miles per hour (mph) 0.621371.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
- Kilometers per hour (km/h) 100 gives Miles per hour (mph) 62.137119.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
- Miles per hour (mph) 62.137119 gives Kilometers per hour (km/h) 100.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
Other questions people ask
How many miles per hour are in a kilometer per hour?
1 kilometer per hour is 0.621371 miles per hour, from the exact unit definitions (NIST SP 811).
How do I convert km/h to mph?
Multiply by 0.621371: mph = km/h × 0.621371192237 (the same as km/h ÷ 1.609344). For example, 1 km/h × 0.621371 = 0.621371 mph.
How do I convert mph back to km/h?
Multiply by 1.609344, or type the miles per hour into the second box and the converter works it out. 1 mile per hour is 1.609344 kilometers per hour.
What is 100 km/h in mph?
62.137119 mph: 100 ÷ 1.609344. 50 km/h is 31.06856 mph, and 120 km/h is 74.564543 mph.
Why divide by 1.609344?
A mile is exactly 1.609344 km: 5,280 feet of 0.3048 m (NIST). Both speeds count per hour, so km/h ÷ 1.609344 = mph.