Speed Converter
Convert speed between kilometres per hour, miles per hour, metres per second, feet per second and knots — instantly, in both directions.
How speed conversion works
Speed is distance per time, so speed units inherit the exact length definitions. Everything here converts
through metres per second:
- 1 km/h = 1/3.6 m/s ≈ 0.2778 m/s (exact, since 1 km = 1,000 m and 1 h = 3,600 s)
- 1 mph = 0.44704 m/s = 1.609344 km/h (exact)
- 1 knot = 1 nautical mile/h = 1.852 km/h ≈ 0.5144 m/s
- 1 ft/s = 0.3048 m/s (exact)
Speedometers, weather reports and flight data mix these freely: road signs use km/h or mph, wind speeds often
come in m/s or knots, and physics problems live in m/s — hence the constant need to convert.
Handy approximations
- km/h → mph: multiply by 0.62 (100 km/h ≈ 62 mph)
- mph → km/h: multiply by 1.6 (60 mph ≈ 97 km/h)
- m/s → km/h: multiply by 3.6 exactly (10 m/s = 36 km/h)
- knots → mph: multiply by 1.15 (20 kn ≈ 23 mph)
Worked example
Converting 100 km/h to mph: 100 ÷ 1.609344 = 62.14 mph. The same speed is
27.78 m/s, 91.13 ft/s, or 54.0 knots.
Frequently asked questions
How do I convert km/h to mph?
Divide by 1.609344, or multiply by 0.6214. So 100 km/h ≈ 62.1 mph, 120 km/h ≈ 74.6 mph, and a UK 70 mph motorway limit is about 112.7 km/h.
What is 100 km/h in metres per second?
Divide km/h by 3.6: 100 km/h = 27.78 m/s. The 3.6 comes from 3,600 seconds per hour divided by 1,000 metres per km — an exact conversion.
How fast is a knot?
1 knot = 1 nautical mile per hour = 1.852 km/h ≈ 1.151 mph. Ships and aircraft use knots because the nautical mile matches one minute of latitude, which simplifies navigation.
Is 30 knots fast for a boat?
30 knots is about 55.6 km/h (34.5 mph) — fast for most leisure boats. Typical cruising yachts do 6–8 knots; fast ferries run 30–40 knots.
What is the speed of sound in these units?
At sea level and 20 °C, sound travels at about 343 m/s — that is 1,235 km/h, 767 mph, or 667 knots. Aircraft speeds relative to it are quoted as Mach numbers.