Speed Converter
Convert km/h, mph, m/s, ft/s, knots, and mach. Useful for cross-border driving and aviation.
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About this tool
Converts between common speed units. Useful when you're driving in the US, reading a weather forecast (winds in km/h vs the boating one in knots), or comparing a jet's mach number to its cruise speed.
Canada vs the US on the road
Canadian speed limits are posted in km/h everywhere. US speed limits are in mph. The most common conversions to remember when driving south:
- 50 mph ≈ 80 km/h
- 55 mph ≈ 89 km/h
- 60 mph ≈ 97 km/h
- 65 mph ≈ 105 km/h
- 70 mph ≈ 113 km/h
- 75 mph ≈ 121 km/h
Most rental cars have dual-marked speedometers — the inner ring shows the other unit. Look for it before you start the trip.
Knots and mach
Knots are nautical miles per hour, used in marine and aviation. 1 knot is exactly 1 nautical mile per hour, or about 1.852 km/h. Mach is the ratio of speed to the speed of sound — Mach 1 is roughly 343 m/s (1,235 km/h) at sea level in 20°C air, but it varies with altitude and temperature. This tool uses the sea-level reference.
Frequently asked questions
- Are knots and km/h the same thing?
- No — 1 knot ≈ 1.852 km/h. The difference comes from the nautical mile (1852 m) being slightly longer than the statute mile (1609.344 m). Marine charts use knots; pilots and sailors get used to them.
- Why does mach depend on temperature?
- The speed of sound depends on the medium it travels through. In air, warmer = faster, denser = faster. So Mach 1 at 35,000 ft (cold, thin air) is about 295 m/s, while Mach 1 at sea level in summer can be over 345 m/s. This tool uses the standard sea-level reference (343 m/s).
- What's the difference between mph and ft/s?
- Both are imperial speed units. 1 mph = 1.4667 ft/s. Engineers and physicists like ft/s because feet are the imperial unit of length; everyday driving uses mph because miles are the everyday distance.
- Why do some places use km/h and others kph?
- Same thing, different abbreviation. The international standard symbol is "km/h". "kph" is informal English. Both mean the same speed.
Last updated: May 17, 2026