Free Online Speed Converter
🔒 Runs in your browser — nothing is sent to a serverSpeed converter for every common unit — meters per second (m/s), kilometers per hour (km/h), miles per hour (mph), knots (kn), feet per second (ft/s) and Mach. Type a value on either side; the result updates instantly. Mach uses the sea-level standard 1 M = 343 m/s (15 °C dry air); actual speed of sound varies with altitude. Everything runs in your browser — nothing is uploaded.
Supported units: Meter per second (m/s), Kilometer per hour (km/h), Mile per hour (mph), Knot (kn), Foot per second (ft/s), Mach (M).
Kilometer per hour (km/h) → Mile per hour (mph)
Quick reference table
| Kilometer per hour (km/h) | Mile per hour (mph) |
|---|---|
| 10 km/h | 6.2137 mph |
| 25 km/h | 15.5343 mph |
| 50 km/h | 31.0686 mph |
| 60 km/h | 37.2823 mph |
| 80 km/h | 49.7097 mph |
| 100 km/h | 62.1371 mph |
| 120 km/h | 74.5645 mph |
| 150 km/h | 93.2057 mph |
| 200 km/h | 124.2742 mph |
Speed unit conversions in everyday life: driving, sailing, aviation
Different domains use different speed units by tradition. Cars and motorcycles outside the US/UK report km/h on the speedometer; in the US it is mph. Marine vessels and aircraft use knots (1 knot = 1 nautical mile per hour) because nautical miles match arc minutes of latitude — handy for chart navigation. Physics and engineering default to m/s; US ballistics, fluid mechanics and HVAC use ft/s. Athletes split times in m/s for sprints (Usain Bolt peaked at 12.4 m/s) and km/h or mph for long-distance pace. Switching between these conventions is a constant practical need: a 100 km/h motorway speed limit is 62 mph; a 130 km/h autobahn cruise is 81 mph; a 250 km/h TGV cruise is 155 mph; a Mach 0.85 airliner cruise is roughly 1,050 km/h or 567 knots.
Why Mach varies with altitude (and why this converter uses sea-level standard)
Mach is not a fixed unit — it is the ratio of an object's speed to the local speed of sound, which depends on air temperature (and therefore altitude). At sea level, ICAO standard atmosphere defines the speed of sound as exactly 340.294 m/s — this converter uses the rounded value 343 m/s commonly cited in aerodynamics textbooks (the difference is under 1 %). At 11 km cruising altitude (-56 °C tropopause), the speed of sound drops to about 295 m/s — so Mach 1 there is about 14 % slower than at sea level. For everyday speed comparisons (e.g. "this jet flies at Mach 0.85") the sea-level approximation is good enough; for accurate flight envelope analysis you need the local atmospheric values. This converter trades precision for predictability: a fixed factor means the same input always gives the same answer.