Speed, Distance & Time Calculator

What this calculates

Choose what you want to find — a distance, a time or a speed — and the unit you want it in, then enter the other two in whatever units you have. This works out the third, with each conversion and the formula shown step by step, and gives the answer in its other units too. A time is also shown in hours, minutes and seconds.

Distances can be in metres, kilometres or miles, times in seconds, minutes or hours, and speeds in metres per second, kilometres per hour or miles per hour. Combinations with no real answer, such as a distance covered in no time, are refused rather than shown as infinity.

The formula

One relationship ties the three quantities together.

Rearranged, it gives the other two.

The units have to agree, so every calculation goes through metres, seconds and metres per second, using exact factors.

A conversion such as 60 km/h to metres per second does not come out as a terminating decimal. The working shows such a figure to ten significant figures, marked ≈, while the calculation itself carries every digit.

Worked example

Ask any other way round and the same journey comes back. Given 120 km and 2 h, the speed is 60 km/h; given 120 km at 60 km/h, the time is 2 h.

Not every answer comes out round. 26.2 mi at 6 mph takes 42,164.8128 m ÷ 2.68224 m/s = 15,720 s, which is 4.366667 h, or 4 h 22 min.

When to use it, and the mistakes to avoid

Use it when planning how long a journey or a run will take, when working out an average speed from a distance and a time, when checking how far you will get at a given speed, and when a figure is given in units you do not think in.

The mistakes that cost the most:

• Mixing units, or writing minutes as a decimal of an hour. At 60 km/h, 30 minutes covers 30 km, because 30 min is 0.5 h. Typing it as 0.30 h gives 18 km — 0.30 h is only 18 minutes. Enter the time in minutes and choose minutes as its unit, and the calculator converts it for you.
• Reading decimal hours as hours and minutes. 4.366667 h is 4 h 22 min, not 4 h 37 min: the part after the point is a fraction of an hour, and 0.366667 of an hour is 22 minutes. That is why the time is also shown in hours, minutes and seconds.
• Averaging two speeds to get the average speed. Drive 60 km at 60 km/h (1 h) and another 60 km at 30 km/h (2 h), and you cover 120 km in 3 h: an average of 40 km/h, not 45 km/h, the average of 60 and 30. The slower leg takes longer, so it counts for more. Work out the total distance and the total time, then divide.
• Getting the m/s and km/h factor the wrong way round. Metres per second to kilometres per hour is × 3.6: 10 m/s is 36 km/h. Going the other way is ÷ 3.6: 60 km/h is 16.66667 m/s. Use the wrong one and the answer is far too small or far too large.
• Expecting an answer from zero time or zero speed. A distance in no time would need unlimited speed, and at zero speed the time would be unlimited, so the calculator refuses both and says why. It also refuses a negative value: speed here is how fast, not which way, and a distance or a time cannot be negative.
• Treating the answer as the whole story of a journey. d = s × t assumes one steady speed, or an average over the whole trip. A real journey speeds up, slows down and stops, so the figures here describe the average, not every moment.

FAQ