Convert speed (km/h, m/s, mph, knots)

The input is multiplied by its factor to metres per second, then divided by the target unit's factor. The factors come from exact definitions: the international mile is 1,609.344 m, the foot 0.3048 m, the nautical mile 1,852 m. No rounded shortcut such as “1 m/s ≈ 3.6 km/h” is used, even though that equality happens to be exact.

v(m/s) = x × kfrom ; y = v(m/s) / kto

1 km/h = 1000 / 3600 m/s = 1/3.6 m/s

1 kn = 1852 / 3600 m/s

The metre per second is the SI derived unit of speed. The nautical mile has been fixed at 1,852 m by international convention since 1929 and is used in marine and air navigation. The mile per hour is based on the international statute mile. Feet per second remain common in ballistics and US engineering.

Value

The speed alone, without the unit, which is picked in the From and To lists.

From

Unit of the speed you entered. The default is kilometres per hour.

To

Unit of the result. The default is metres per second, the SI unit.

Assumptions

• A knot is one nautical mile (1,852 m) per hour.
• Miles per hour use the international statute mile (1,609.344 m).
• The factors are exact; only the display rounds.

Limits

• No Mach number: the speed of sound depends on temperature and altitude.
• No relativistic speeds and no Lorentz correction.
• An average speed is not an instantaneous speed.

27.78 m/s and 100 km/h describe the same speed. A gap between your GPS and the car's speedometer does not come from the conversion but from the legal tolerance on speedometers, which must never read low. At sea, mistaking knots for km/h skews an arrival estimate by about 85%.

• Treating a knot as a statute mile per hour.

  1 kn = 1.852 km/h, not 1.609 km/h.

• Writing “knots per hour”.

  A knot is already a speed: one nautical mile per hour.

• Dividing a distance by a time without matching the units.

  Convert distance and duration first, then divide.

• Length converterEvery value goes through the meter, then to the target unit. The inch is 25.4 mm exactly since the 1959 agreement, as in the NIST SI conversion factors.
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• Speed, distance, timeTwo known quantities, the third follows. Kilometres and km/h, or miles and mph, but not a mix of the two systems.
• Weight (mass) converterEveryday speech says “weight”; SI speaks of mass. Conversion goes through the kilogram. The pound (lb) is 0.45359237 kg exactly, a NIST factor, not a weighing on Earth.
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Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.

• NIST Guide to the SI, Appendix B: Conversion Factors — National Institute of Standards and Technology
• The International System of Units (SI) — Bureau international des poids et mesures (BIPM)