MPH vs KM/H: Speed Units Compared
Key Difference
1 mph = 1.60934 km/h. Miles per hour is used for speed limits in the US and UK. Kilometers per hour is the standard in the rest of the world. A 60 mph speed limit is roughly equivalent to 100 km/h.
Side-by-Side Comparison
| Property | MPH | KM/H |
|---|---|---|
| Full name | Miles per hour | Kilometers per hour |
| Symbol | mph (or mi/h) | km/h (or kph) |
| System | Imperial / US Customary | Metric |
| Used in | USA, UK, Myanmar, some Caribbean | Rest of the world (~190 countries) |
| Common uses | Road speed limits, car speedometers | Road speed limits, weather, athletics |
| Conversion | 1 mph = 1.60934 km/h | 1 km/h = 0.62137 mph |
Where Each Is Used
MPH is used for road speed limits and speedometers in the United States, the United Kingdom, and a handful of smaller territories (Bahamas, Myanmar, Antigua and Barbuda, Samoa). Despite using miles for road distances, British car speedometers display both mph and km/h.
KM/H is the standard in all other countries, covering over 90% of the world's roads. European speed signs show km/h. Rental cars in Europe, Asia, South America, Africa, and Oceania have speedometers primarily in km/h, though many include a smaller mph scale for dual-market vehicles.
Wind speeds are reported differently by context. Meteorologists use km/h in most countries, mph in the US and UK, and knots (nautical miles per hour) for marine and aviation forecasts worldwide. The Beaufort scale provides a universal reference independent of units.
Conversion Formulas
MPH to KM/H
km/h = mph × 1.60934
Example: 70 mph = 70 × 1.60934 = 112.65 km/h
KM/H to MPH
mph = km/h × 0.62137
Example: 120 km/h = 120 × 0.62137 = 74.56 mph
Speed Limits Around the World
| Context | MPH | KM/H |
|---|---|---|
| Residential area (US) | 25 | 40 |
| City street (typical) | 30-35 | 50 |
| US highway | 55-65 | 90-105 |
| UK motorway | 70 | 113 |
| European motorway | 75-81 | 120-130 |
| German Autobahn (advised) | 81 | 130 |
| Average walking speed | 3.1 | 5 |
| World-class marathon pace | 13 | 21 |
When to Use Which
Use mph when driving in the US or UK, discussing American or British speed limits, or reading US weather reports that give wind speeds in mph.
Use km/h when driving anywhere else in the world, discussing speed with international audiences, or in scientific and engineering contexts. Most countries post speed limits in km/h.
Quick mental shortcut: multiply mph by 1.6 to get km/h, or multiply km/h by 0.6 to get mph. For example, 100 km/h × 0.6 = 60 mph (actual: 62.1). Another trick: 5 mph ≈ 8 km/h, so count by fives in mph and eights in km/h.
A Brief History
Miles per hour became a formal unit of speed measurement as road travel expanded in the 18th and 19th centuries. Early speed limits were set in mph in Britain and the US. The first national speed limit in the UK was 20 mph in 1903 under the Motor Car Act. The US adopted mph for all road signs and speedometers.
Kilometers per hour followed the global adoption of the metric system. As countries metricated throughout the 19th and 20th centuries, they switched road signs from miles to kilometers. Canada completed its conversion from mph to km/h in 1977. Australia switched in 1974. The process was straightforward: speed limit signs were updated and speedometers were changed to read km/h.