To convert km/h to mph, multiply by 0.62137. 1 km/h equals 0.62137 mph, about 20% of walking pace.
| km/h | mph |
|---|---|
| 1 km/h | 0.62137 mph |
| 2 km/h | 1.2427424 mph |
| 5 km/h | 3.106856 mph |
| 10 km/h | 6.2137119 mph |
| 25 km/h | 15.53428 mph |
| 50 km/h | 31.06856 mph |
| 100 km/h | 62.137119 mph |
| 250 km/h | 155.3428 mph |
| 500 km/h | 310.6856 mph |
| 1000 km/h | 621.37119 mph |
Definition: How many kilometers you'd cover in an hour at a constant speed.
History: It's less a unit with its own origin story and more a natural pairing - once the kilometer became the standard distance unit almost everywhere, km/h followed automatically as the speed unit that goes with it, showing up on speedometers and road signs worldwide.
Current use: Virtually every country's speed limits are posted in km/h - the US, UK, and Myanmar are the notable holdouts still using mph on their roads.
Definition: How many miles you'd cover in an hour at a constant speed.
History: mph rode along with the mile's persistence in English-speaking countries - it's been the standard way to describe speed since the horse-and-carriage era, and just carried over once cars replaced horses.
Current use: Road speed limits and car speedometers in the US and UK. Aircraft speed usually uses knots instead, even in these countries.
The factor is 0.621371, which is derived rather than defined, so any decimal you see has been rounded somewhere.
For a quick estimate, multiply by 0.6. That is off by about 3.4%, which is fine for a rough figure and not fine for anything you are paying for or building to. Use the exact factor of 0.621371 when it matters.
Going the other way, one mph is 1.609 km/h, which is usually the easier direction to work in. Because the forward factor is small, watch the decimal place rather than the digits: a factor-of-ten slip is the common error, not a rounding one.
To anchor the scale: 2 km/h is about 1.24 mph.
Want a real-world stress test for this converter? See how fast F1 cars actually go, in both units.