Speed Converter
Convert between km/h, mph, m/s, knots, and Mach number instantly.
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How to use this calculator
- 1
Enter the speed value you want to convert.
- 2
Select the unit you are converting from (e.g. km/h).
- 3
Select the unit you want the result in (e.g. mph).
- 4
The result appears instantly.
Frequently asked questions
How do I convert km/h to mph?
Multiply km/h by 0.621371 to get mph. For example, 100 km/h = 62.14 mph.
How do I convert mph to km/h?
Multiply mph by 1.60934 to get km/h. For example, 60 mph = 96.56 km/h.
What is a knot in km/h?
One knot equals 1.852 km/h or approximately 1.151 mph. Knots are used in maritime and aviation contexts.
What is Mach 1 in km/h?
Mach 1 equals the speed of sound, which is approximately 1,235 km/h (767 mph) at sea level at 15°C. It varies with altitude and temperature.
How fast is the speed of light in km/h?
The speed of light in a vacuum is approximately 1,079,252,848 km/h or about 299,792,458 metres per second.
Speed and velocity conversion
Common speed measurement systems
Speed is the distance travelled per unit of time. The metric system uses metres per second (m/s) as the SI base unit, while km/h is used for road speeds in most countries. The US and UK use miles per hour (mph) for road travel. Aviation and maritime navigation use knots. Aerospace uses Mach numbers.
Key speed conversion factors
1 km/h = 0.6214 mph | 1 mph = 1.6093 km/h | 1 m/s = 3.6 km/h = 2.237 mph | 1 knot = 1.852 km/h | Mach 1 ≈ 1,235 km/h at sea level.
Speed in everyday life
Speed conversions matter for international drivers (different speed limit systems), pilots and sailors (knots vs km/h), athletes (running pace in min/km vs min/mile), and physics calculations. A car travelling at 100 km/h is going 62.1 mph — knowing the conversion prevents confusion when crossing borders.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →