Speed Converter

How it works

Speed conversions translate between common rate units: miles per hour (mph), kilometers per hour (km/h), meters per second (m/s), feet per second (ft/s), and knots (nautical miles per hour, used in aviation and maritime contexts). The exact ratios are 1 mph = 1.609 km/h = 0.447 m/s = 1.467 ft/s = 0.869 knots.

Some useful approximations: 1 m/s ≈ 2.24 mph; the speed of sound in air is roughly 343 m/s ≈ 768 mph; the speed of light is 299,792,458 m/s ≈ 670 million mph; a comfortable walking pace is about 3 mph or 5 km/h; freeway speeds are 60–75 mph or 100–120 km/h.

In aviation, "knots" remains standard because 1 knot = 1 nautical mile per hour, and 1 nautical mile is exactly 1 minute of latitude — so navigation math works cleanly with knots in nautical contexts. Pilots also use Mach number for high-speed aircraft (Mach 1 = local speed of sound, which varies with altitude and temperature).

Cars in the US use mph; most of the world uses km/h. The two-thirds approximation (mph ≈ 2/3 of km/h) is close but slightly low — a sign showing 100 km/h is about 62 mph, not the rough 66 you'd get from 2/3.

Wind speed in weather forecasts varies: m/s in many countries, mph in the US, km/h in most of Europe, and knots for marine forecasts. The Beaufort scale describes wind in semi-qualitative terms ("light breeze" 4–7 knots, "strong gale" 41–47 knots) and is still used for sailing.

For pace conversions (running, cycling), invert speed: a 6 mph running pace is a 10-minute mile or 6.2-minute kilometer. Many racing apps display both pace (min/km or min/mi) and speed (km/h or mph) — they're reciprocals scaled by the units.