What this calculator does
Turn a speed in miles per hour into kilometers per hour, or the other way around, in one step. Miles per hour (mph) is the road-speed unit in the United States and the United Kingdom. Kilometers per hour (km/h) is used on road signs and speedometers nearly everywhere else. You'll need to switch between them when you rent a car abroad, compare treadmill settings or read a foreign car review.
One mile is exactly 1,609.344 meters. So one mile per hour is exactly 1.609344 kilometers per hour, and a kilometer per hour is about 0.621 mph. Both speeds are measured per hour, so converting a speed uses the very same number as converting miles to kilometers.
Where it's used
Why this math matters outside the classroom:
- Driving abroad. A 100 km/h speed limit in Europe is about 62 mph.
- Running pace. A runner at 6 mph is moving at about 9.66 km/h.
- Car specs. A top speed of 155 mph is about 249 km/h.
- Cycling. Cyclists comparing ride logs see that an average of 20 mph is about 32.2 km/h.
- Wind gusts. Forecasters giving wind gusts of 50 mph to a metric audience report about 80 km/h.
Grade level and standards: Grades 5–6; Common Core State Standards for Mathematics 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter a speed. Decimals are fine.
- Choose mph to km/h, or km/h to mph.
- Read the converted speed, the working and the table of typical speeds in the direction you chose.
What the inputs mean
- Value to convert
- A speed in miles per hour (for mph → km/h) or kilometers per hour (for km/h → mph).
- Direction
- Which way to convert.
Formula and method
km/h = mph × 1.609344 mph = km/h ÷ 1.609344 ≈ km/h × 0.621371192237
A mile is officially 5,280 feet, and each foot is exactly 0.3048 m. That makes a mile exactly 1,609.344 m. So multiplying mph by 1.609344 gives an exact answer.
The reverse number, 0.621371…, has decimals that never end. So to go from km/h to mph, the calculator divides by 1.609344 instead.
Worked example
A US highway sign shows 60 mph. What is that in km/h?
- The conversion number is exact: 1 mph = 1.609344 km/h.
- 60 × 1.609344 = 96.56064.
Result: 60 mph is 96.56064 km/h, just under 97 km/h.
Understanding the result
A shortcut you can do in your head for mph to km/h: multiply by 1.6, or add 60%. 60 mph becomes 96 km/h, about 0.6% low. For km/h to mph, multiply by 5/8. 100 km/h becomes 62.5 mph, against the exact 62.14, about 0.6% high.
Speeds people often look up: 30 mph is 48.28 km/h; 70 mph is 112.65 km/h; 50 km/h is 31.07 mph; 120 km/h is 74.56 mph. These are conversions only. Always follow the posted limit, in the units the sign uses.
One easy mistake is reading the wrong scale on a speedometer that shows both. Most cars show mph and km/h together, with one scale in smaller print. So 100 on the inner ring may be km/h, not mph.
Assumptions and limitations
- The mile is the standard international mile of 1,609.344 m.
- Speeds are steady (average) speeds over an hour of time.
- Nautical miles per hour (knots) are a different unit. Use the knots to mph page for boats and aircraft.
- Converting a speed doesn't convert a fuel economy figure such as miles per gallon.
Frequently asked questions
How many km/h is 1 mph?
Exactly 1.609344 km/h.
Is kph the same as km/h?
Yes. "kph" is an informal short form, and km/h is the standard metric symbol. Both mean kilometers per hour.
How do I convert a running pace instead of a speed?
Pace is time per distance, the flip side of speed. Convert the speed first, then work out 60 ÷ speed to get minutes per mile or per kilometer. The pace calculator does this for you.
How this calculator is checked
Method: International mile = 5,280 ft × 0.3048 m = 1,609.344 m exactly, so 1 mph = 1.609344 km/h. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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