Speed Calculator

How to use the speed calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

Speed, distance and time are one relationship read three ways, and this solves for whichever one you leave out. The arithmetic is trivial; the mistakes are all in the units, so everything is converted internally and reported in several at once.

Pace is given alongside because it is how running and cycling are actually discussed. Speed and pace are reciprocals — 12 km/h is 5 minutes per kilometre — and the inversion trips people up more often than it should, particularly when comparing a pace in minutes per mile against a speed in kilometres per hour.

The number worth understanding is average speed, because it is not the average of your speeds. Driving somewhere at 60 and returning at 40 gives an average of 48, not 50: you spend more time at the slower speed, so it weighs more heavily. That is the harmonic mean, and it is why a delay costs more time than an equivalent stretch of fast driving saves.

For the same reason, small increases in speed save less time than they seem to. Raising a two-hour drive from 100 to 110 km/h saves about eleven minutes, and the saving shrinks with every further increment while the risk does not.

Common uses

• Working out how long a journey will take at a given speed.
• Converting a running pace into a speed, or back.
• Checking the average speed of a completed trip.

Frequently asked questions

How do I convert speed to pace?

Divide 60 by the speed in kilometres per hour to get minutes per kilometre. They are reciprocals, so 12 km/h is 5 minutes per kilometre.

Is average speed the average of my speeds?

No. Out at 60 and back at 40 averages 48, not 50, because more time is spent at the slower speed. That is the harmonic mean.

How much time does driving faster save?

Less than expected, and progressively less. Raising a two-hour drive from 100 to 110 km/h saves about eleven minutes, and each further increase saves less again.