Convert any speed between six units: metres per second, kilometres per hour, miles per hour, feet per second, knots, and Mach. All factors are exact SI-derived values except Mach, which uses the sea-level 20°C speed of sound (343 m/s) as a reference — a simplification surfaced in the UI whenever Mach is selected.
Exact conversion factors
| Unit | m/s equivalent | Notes |
|---|---|---|
| m/s | 1 | base |
| km/h | 1000/3600 = 5/18 ≈ 0.2778 | exact rational |
| mph | 1609.344/3600 = 0.44704 | exact (1959 mile definition) |
| ft/s | 0.3048 | exact (1959 foot definition) |
| knot | 1852/3600 ≈ 0.5144 | exact (international nautical mile) |
| Mach | 343 | sea-level 20°C simplification |
Every factor except Mach is exact (subject to floating-point representation). Mach varies with altitude and temperature; the tool uses sea-level reference with a visible note when Mach is in either slot.
Example: US speed limit to metric
60 mph speed limit: 60 × 1.609344 = 96.56 km/h. Commonly rounded to 96 km/h on reciprocal signage. 70 mph = 112.65 km/h. 75 mph = 120.70 km/h. 55 mph = 88.51 km/h.
Mental arithmetic: mph × 1.6 is close enough for most conversions, or mph × 8 / 5 for the exact ratio.
Example: aviation
Cruise speed for a typical commercial jet is about 0.82 Mach at cruising altitude — but the tool’s sea-level Mach gives you 0.82 × 343 = 281 m/s = 1012 km/h = 629 mph, which is close to the ground speed but not exactly right because of altitude correction. The actual indicated airspeed at cruise is around 450–480 knots (833–889 km/h). The tool is useful for rough conversion but real aviation calculations need local temperature and altitude.
Example: maritime
A container ship doing 20 knots: 20 × 1.852 = 37.04 km/h = 23.02 mph. For distance calculations, 20 knots × 24 hours = 480 nautical miles per day = 889 km/day.
Example: wind speed
Beaufort scale references: a gentle breeze is 3–5 m/s (11–19 km/h, 7–12 mph), a strong gale is 20–25 m/s (72–90 km/h, 45–56 mph), a hurricane starts at 33 m/s (119 km/h, 74 mph). Weather services use km/h or mph depending on region; aviation uses knots; marine forecasts often mix km/h and knots. The tool handles all four.
Mach and the speed of sound
The speed of sound depends on the medium and its temperature. In dry air at 20°C at sea level, it’s 343 m/s. At 0°C, it drops to 331 m/s. At −56°C (typical stratospheric cruise temperature), it’s 295 m/s. The tool uses 343 m/s throughout because that’s the most common reference; a real Mach-to-real-speed conversion would need local atmospheric conditions.
Supersonic reference: Mach 1 is the sound barrier, broken by Chuck Yeager in 1947. Commercial supersonic flight (Concorde) cruised at Mach 2.04 ≈ 700 m/s at altitude. The SR-71 Blackbird hit Mach 3.3 ≈ 1100 m/s. The X-15 rocket plane reached Mach 6.7 ≈ 2300 m/s.
What this tool does not do
It doesn’t do altitude-corrected Mach. Real Mach needs local speed of sound, which the tool doesn’t compute.
It doesn’t convert between angular and linear speed. “RPM to m/s” needs the radius, which this tool doesn’t know about.
It doesn’t handle natural-language speeds. Enter a number, not “70 mph”.
It doesn’t include furlongs per fortnight or other historical / joke units. The six standard units cover almost every real use case.
It doesn’t compute acceleration, distance, or time. Speed × time = distance and so on are kinematics problems; this is pure unit conversion. For the length side the length converter handles mi ↔ km ↔ m; for the time side the time unit converter handles hours ↔ seconds.