Speed Converter

Speed measures distance traveled per unit of time. Most countries use kilometers per hour (km/h) for road travel, but the United States and the United Kingdom use miles per hour (mph). This creates a constant need for conversion when driving internationally, reading foreign vehicle specifications, following motorsport from another country, or interpreting weather reports that reference wind speeds in different units.

Knots are used in aviation and maritime navigation worldwide, and this has not changed despite metrication elsewhere. One knot equals exactly one nautical mile per hour. A nautical mile is defined as 1/60 of a degree of latitude, approximately 1.852 kilometers or 1.151 miles. This ties directly to navigation on a geographic coordinate grid, which is why pilots and ship captains have always used knots — the unit is built into how latitude and longitude work.

Scientists use meters per second (m/s) as the SI unit for speed. Mach number expresses speed relative to the speed of sound, which varies with altitude and temperature: at sea level and 15°C, Mach 1 equals approximately 340 m/s (1,225 km/h, or 761 mph). The speed of light in a vacuum, exactly 299,792,458 m/s, is used as a fundamental constant in physics.

Speed conversions matter for international drivers renting cars abroad, pilots monitoring airspeed in knots while altimeters read in feet, engineers comparing vehicle specs from foreign manufacturers, athletes and coaches comparing performance data from competitions held under different measurement conventions, and anyone following Formula 1, Tour de France, or other international sports where speeds are reported in metric.