Speed limits, weather reports, and vehicle specs use different units depending on the country and context. This converter handles the four most common speed units using meters per second as the internal reference point.
Conversion factors used
| Unit | Meters/second equivalent |
|---|---|
| 1 km/h | 0.277778 m/s |
| 1 mph | 0.44704 m/s |
| 1 knot | 0.514444 m/s |
Worked examples
| From | To | Result |
|---|---|---|
| 100 km/h | mph | 62.14 mph |
| 60 mph | km/h | 96.56 km/h |
| 20 knots | km/h | 37.04 km/h |
See our metric vs. imperial conversion guide for the same conversion logic applied to length, weight, and temperature.
Where each unit is commonly used
- km/h: most countries' road speed limits and vehicle speedometers.
- mph: road speed limits in the United States and United Kingdom.
- m/s: scientific and engineering contexts, including wind speed in some meteorological contexts.
- Knots: maritime and aviation navigation, based on nautical miles per hour.
A real-world mix-up
A driver from the US renting a car in Europe will see speed limit signs in km/h while their instincts are calibrated to mph — misreading a "120" sign as if it were mph rather than km/h would mean driving at roughly double the legal, and safe, limit. The reverse trips up European drivers renting cars in the US or UK, where a "70" sign means mph, not km/h. Because both numbers look like ordinary two- or three-digit figures, the unit label is easy to skim past, which is exactly why rental car dashboards in some countries display both scales side by side.
References
- National Institute of Standards and Technology (NIST) — official unit definitions
Frequently asked questions
How do I convert km/h to mph?
Multiply the km/h value by approximately 0.62137 to get mph.
What is a knot?
A knot is one nautical mile per hour, equal to about 1.852 km/h, used primarily in maritime and aviation navigation.
How do I convert m/s to km/h?
Multiply the m/s value by 3.6 to get km/h.
Why does the US still use mph instead of km/h?
The US began a voluntary shift toward the metric system in the 1970s, but road signage was excluded due to the cost of replacing millions of signs and retraining drivers, so mph remained the legal standard for speed limits.