Speed, Distance & Time Calculator

Speed, distance and time

Speed is how much distance you cover in a given time, and that single relationship rearranges three ways depending on which value you're missing.

v = d / t  ·  d = v × t  ·  t = d / v

This calculator handles all three, and lets you mix units — enter a distance in kilometres and a time in hours to get a speed in km/h, or work in metres and seconds for m/s. Internally everything converts to SI first, so the combinations always agree.

Average vs instantaneous speed

What this works out is average speed over the whole journey — total distance divided by total time. It isn't the speed at any particular moment. A car that averages 75 km/h over two hours may have sat still in traffic and later driven at 120; the average smooths all of that away, which is exactly what you want for planning a journey and not what you want for reading a speedometer.

Worked example

A 150 km drive taking 2 hours averages 150 / 2 = 75 km/h, which is about 20.8 m/s or 46.6 mph. Turn it around: at 75 km/h, covering 300 km takes 300 / 75 = 4 hours. A runner doing 10 km in 50 minutes averages 12 km/h — or in the runner's own terms, a 5-minute kilometre, which thepace calculator handles directly.

Average speed is not instantaneous speed

This calculates an average over the whole journey, which is rarely the speed at any particular moment. A trip averaging 50 km/h may have included motorway sections at 120 and a stationary half-hour in traffic. The distinction matters when the average is used to infer something about the journey — an average below a limit does not demonstrate that the limit was never exceeded, and a journey time built from an assumed average will be optimistic if it ignores stops.