Speed Converter
Quick Conversions
Related Converters
Understanding Speed Units
Common Speed Units
Kilometers per hour (km/h)
Standard unit for road speeds in most countries. Used on speedometers outside the US/UK.
Miles per hour (mph)
Used for road speeds in US, UK, and a few other countries. 1 mph ≈ 1.609 km/h.
Meters per second (m/s)
SI unit for speed. Used in science and engineering. 1 m/s = 3.6 km/h.
Knots (kn)
Used in aviation and maritime navigation. 1 knot = 1 nautical mile per hour = 1.852 km/h.
The Mach Number
Mach number is the ratio of an object's speed to the speed of sound in the surrounding medium. Mach 1 is the speed of sound, which varies with temperature and altitude.
Speed Regimes
- Subsonic: Below Mach 0.8 (most commercial aircraft)
- Transonic: Mach 0.8 - 1.2 (approaching sound barrier)
- Supersonic: Mach 1.2 - 5 (Concorde, fighter jets)
- Hypersonic: Above Mach 5 (spacecraft re-entry)
Speed Comparisons
| Object/Activity | km/h | mph | m/s |
|---|---|---|---|
| Walking | 5 | 3.1 | 1.4 |
| Running (sprint) | 37 | 23 | 10.3 |
| City driving | 50 | 31 | 13.9 |
| Highway driving | 120 | 75 | 33.3 |
| Commercial jet | 900 | 560 | 250 |
| Speed of sound | 1,235 | 767 | 343 |
| Space station | 27,600 | 17,150 | 7,660 |
Conversion Formulas
mph = km/h × 0.6214
km/h = mph × 1.609
m/s = km/h ÷ 3.6
knots = km/h ÷ 1.852
Why Knots?
Sailors historically measured speed by throwing a log overboard attached to a rope with knots tied at regular intervals. They counted how many knots passed through their hands in a set time, giving rise to the term "knots" for nautical speed.
Frequently Asked Questions
How do I convert mph to km/h?
Multiply miles per hour by 1.609 to get kilometers per hour. For example, 60 mph × 1.609 = 96.56 km/h. To convert km/h to mph, multiply by 0.6214 (or divide by 1.609).
What is a knot and why is it used in aviation?
A knot equals one nautical mile per hour (1.852 km/h or 1.151 mph). Aviation and maritime industries use knots because nautical miles are based on Earth's geometry—one nautical mile equals one minute of latitude, making navigation calculations simpler.
What is Mach 1 and does it change?
Mach 1 is the speed of sound, which varies with temperature and altitude. At sea level and 20°C (68°F), Mach 1 is approximately 1,235 km/h (767 mph). At higher altitudes where air is colder, the speed of sound decreases.
What's the difference between speed and velocity?
Speed is a scalar quantity measuring how fast something moves (e.g., 50 km/h). Velocity is a vector that includes both speed and direction (e.g., 50 km/h north). For unit conversion purposes, speed and velocity use the same units.