How to convert km/h to mph
mph = km/h × 0.6213711922. The scale factor is the source-unit factor divided by the destination-unit factor.
Worked example
A speed of 100 km/h converts to 62.13711922 mph.
- Start with 100 km/h.
- Multiply 100 by 0.6213711922.
- Report 62.13711922 mph, rounded to the precision of your original measurement.
Divide by 1.609344. The result is a unit conversion, not a change to a posted speed limit.
Check the reverse conversion
1 mph = 1.609344 km/h. Use the mile per hour to kilometer per hour converter to calculate in the opposite direction. This has its own formula and reference table.
Definitions that matter
A knot is one international nautical mile per hour, not one mile per hour. Speed conversion does not calculate acceleration or journey time.
The base unit for this category is m/s. One km/h corresponds to 0.2777777778 mps; one mph corresponds to 0.44704 mps. These definitions explain the relationship rather than relying on a rounded display value.
Sources and precision
Definitions: NIST Guide to the SI. Calculations use double precision; the tool defaults to a readable rounded result, while tables show up to ten significant digits. Displaying more digits does not increase the accuracy of the original measurement.
Read our calculation methodology and content standards, or continue with distance and time units across measurement systems.