How speed units relate
Speed is distance divided by time. One kilometer per hour equals exactly 1/3.6 meter per second. One international mile equals exactly 1,609.344 meters, so one mile per hour equals exactly 0.44704 meter per second.
Knots and navigation
A knot is one nautical mile per hour. The international nautical mile is exactly 1,852 meters, making one knot approximately 1.15078 mph or exactly 1.852 km/h. Knots are standard in marine and aviation contexts.
Speed is not pace
Speed measures distance covered per unit of time. Pace reverses that relationship and reports time per unit of distance, such as minutes per kilometer. Use the running pace calculator when you need pace or split planning.
Check a road-speed conversion
For 100 km/h, divide by 3.6 to obtain about 27.7778 m/s. Dividing that value by the exact 0.44704 m/s in one mph gives about 62.1371 mph. Converting 62.1371 mph back should return nearly 100 km/h; a small difference comes from displaying rounded digits. Keep more digits internally and round the final result to match the precision of the source speedometer, sign, log, or specification.
State what is moving relative to what
A unit conversion preserves the numerical physical quantity but not its context. Ground speed, airspeed, water speed, wind speed, and closing speed can describe different frames of reference. A boat moving at 10 knots through water does not necessarily travel over the ground at 10 knots when current is present. Likewise, a vehicle’s average trip speed is not its instantaneous speed. For formal factors, compare the selected units with the NIST speed and velocity conversion table.
This converter changes units only. Posted limits, instrument accuracy, wind, current, and relative motion require their own context.