Velocity Conversion Calculator

The Velocity Conversion Calculator converts speed values between six common units: metres per second, kilometres per hour, miles per hour, feet per second, knots, and Mach number. Velocity — the rate of change of position — is one of the most frequently measured quantities in physics, engineering, and everyday life.

The SI unit of velocity is metres per second (m/s). However, different contexts demand different units. Road speed limits use km/h (metric countries) or mph (US, UK). Aviation and maritime navigation use knots (nautical miles per hour). Aerospace and ballistics use Mach numbers, which express speed relative to the local speed of sound. Engineering calculations often involve ft/s in US customary units.

The fundamental conversion relationships are:

$$1\text{ m/s} = 3.6\text{ km/h} = 2.23694\text{ mph} = 3.28084\text{ ft/s}$$

$$1\text{ knot} = 0.514444\text{ m/s} = 1.852\text{ km/h}$$

$$\text{Mach } 1 = 343\text{ m/s (at 20 °C in dry air)}$$

The knot derives from the nautical mile, which is defined as one minute of arc of latitude along Earth's surface (1852 m exactly). This makes knots especially convenient for navigation — a ship traveling at 10 knots covers 10 nautical miles (10 minutes of latitude) per hour.

The Mach number is the ratio of an object's speed to the local speed of sound: $$Ma = v / c$$, where $$c = \sqrt{\gamma R T / M}$$ depends on temperature, gas composition, and the adiabatic index $$\gamma$$. At sea level and 20 °C in dry air, $$c \approx 343$$ m/s. This calculator uses that standard value; actual Mach numbers at altitude or different temperatures will differ.

Enter a value, choose the source unit, and the calculator displays the equivalent in all six units simultaneously — ideal for physics problems, travel planning, pilot reference, and engineering design.