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Convert m/s, km/h, mph, ft/s, and knots. Used for travel, aviation, and physics calculations.
The SI unit of speed is metres per second (m/s). It is used in physics equations, engineering calculations, and scientific literature. One metre per second equals 3.6 km/h, which is roughly walking pace for a person. The speed of sound in air at 20°C is approximately 343 m/s. The speed of light in a vacuum is 299,792,458 m/s, which defines the metre itself.
Kilometres per hour (km/h) is the dominant unit for road transport in most of the world. Road signs, speedometers, and speed limits in Europe, Asia, and most of the Americas use km/h. Miles per hour (mph) is used in the United States, the United Kingdom, and a handful of other countries. One mph equals 1.60934 km/h.
Knots are the standard unit in aviation and maritime navigation. One knot equals one nautical mile per hour, and one nautical mile equals 1,852 metres. This means 1 knot = 1.852 km/h = 1.15078 mph. Knots are used because nautical miles tie directly to degrees of latitude, making navigation calculations cleaner on charts and in flight planning software.
Feet per second (ft/s) appears in US ballistics and in some engineering contexts, particularly in the United States. A bullet travelling at 2,700 ft/s is moving at about 823 m/s or roughly 2.4 times the speed of sound. Feet per second is also used in US water flow calculations and HVAC air velocity specs.
A few reference speeds are useful for calibrating intuition. A fast walking pace is about 5 km/h (1.4 m/s). A recreational cyclist averages around 20 km/h (12.4 mph). A car on a motorway travels at 100-130 km/h (62-81 mph). A commercial airliner cruises at around 900 km/h (559 mph or 486 knots). A low-Earth-orbit satellite travels at roughly 7,800 m/s (28,080 km/h).
Why do pilots use knots instead of km/h or mph?
One knot equals one nautical mile per hour, and one nautical mile equals one minute of arc on the Earth's surface. This ties airspeed directly to geographic coordinates, making distance calculations straightforward during navigation without unit conversions.
How do I convert km/h to m/s?
Divide by 3.6. One km/h = 1,000 m / 3,600 s = 1/3.6 m/s. So 90 km/h = 25 m/s. To go from m/s to km/h, multiply by 3.6.
What does Mach 1 mean in km/h?
Mach 1 is the speed of sound, which varies with altitude and temperature. At sea level at 20°C it is approximately 1,235 km/h (768 mph or 667 knots). At cruising altitude (-56°C) the speed of sound drops to about 1,062 km/h (660 mph), which is why airliners cruise near Mach 0.85 while still covering ground quickly.