Speed Converter

How It Works

Speed is distance divided by time. This converter uses meters per second (m/s) as its base unit and stores a factor for each unit representing its value in m/s. Converting from one speed to another multiplies by the source's m/s factor and divides by the target's.

Kilometers per hour (km/h) is the standard road speed unit in most countries. 1 km/h = 1,000 m ÷ 3,600 s = 0.27778 m/s. The conversion between km/h and mph (miles per hour) is a ratio of the length units: 1 mile = 1.60934 km, so 1 mph = 1.60934 km/h = 0.44704 m/s.

The knot (kn) is the speed unit of maritime and aeronautical navigation, equal to one nautical mile per hour. A nautical mile is 1,852 meters (the length of one arcminute of latitude), making 1 kn = 1,852 ÷ 3,600 = 0.514444 m/s. Meteorologists also use knots for wind speed in aviation forecasts.

Mach number expresses speed relative to the speed of sound. The speed of sound varies with air temperature and density — at sea level and 15°C (standard atmosphere), sound travels at approximately 343 m/s (1,235 km/h or 767 mph). Mach 1 = 343 m/s. This converter uses 343 m/s as the Mach factor, appropriate for sea-level conditions.

Worked example — Motorway speed limit:
UK motorway limit: 70 mph. In km/h: 70 × 1.60934 = 112.65 km/h. German Autobahn recommended speed: 130 km/h = 130 × 0.27778 = 36.11 m/s = 80.78 mph.

Worked example — Commercial aircraft:
A Boeing 737 cruises at about 840 km/h. In knots: 840 ÷ 1.852 = 453.6 kn. In Mach: 840 ÷ (343 × 3.6) = 0.68 Mach.

Worked example — Wind speed in a storm:
Hurricane-force winds start at 64 kn (Beaufort scale 12). In km/h: 64 × 1.852 = 118.5 km/h. In mph: 64 × 1.15078 = 73.6 mph.

Worked example — Running pace:
A 4-minute kilometre pace = 1 km ÷ 240 s = 4.167 m/s = 15 km/h = 9.32 mph.

The foot per second (ft/s) is used in ballistics and some engineering contexts. 1 ft/s = 0.3048 m/s (since 1 ft = 0.3048 m). A bullet travelling at 3,000 ft/s = 914.4 m/s ≈ 2.67 Mach.