Speed Distance and Time Calculator

What the speed distance time calculator does

Speed, distance, and time are tied together by a single relationship, and if you know any two of them, the third is fixed. This tool does exactly that. You pick the one you are missing, enter the other two, and it works it out.

It is built to be flexible rather than tied to cars. The distance can be in kilometers, miles, yards, feet, or meters, the speed in any of the matching units, and the time down to the second, so it handles a homework problem about a train just as happily as a real journey.

How to use it

1. Choose a calculation. Find Time, Find Speed, or Find Distance, depending on which one you do not know.
2. Enter the other two. The boxes change to ask for exactly what is needed. Pick the units next to each value, and for time use the hours, minutes, and seconds boxes.

Press Calculate for the answer, or Reset to clear it and start again.

The one formula, three ways

There is really only one equation here, and the other two are just it rearranged. Speed is distance divided by time:

Speed = distance ÷ time

Shuffle that around and you get the other two. If you know the speed and the time and want the distance, you multiply:

Distance = speed × time

And if you know the distance and the speed and want the time, you divide the other way:

Time = distance ÷ speed

Some people picture it as a triangle with distance on top and speed and time underneath. Cover the one you want and the triangle shows you whether to divide or multiply. The calculator just does the right one of these three for you once you pick what you are solving for.

A worked example of each

One for each direction, so the pattern is clear.

Finding time

A car covers 150 km at a steady 50 km/h. Time = 150 ÷ 50 = 3 hours.

Finding speed

A sprinter runs 300 meters in 40 seconds. Speed = 300 ÷ 40 = 7.5 meters per second.

Finding distance

A train holds 60 mph for 2.5 hours. Distance = 60 × 2.5 = 150 miles.

Same relationship every time. The only thing that changes is which value you start without.

Keeping your units straight

The one place this goes wrong is units that do not match. Speed is always a distance over a time, so the units inside it have to line up with the distance and time you are using. If your distance is in kilometers, your speed needs to be in kilometers per hour, not miles per hour, or the answer comes out wrong by the conversion factor. The calculator lets you pick units on each field and lines them up for you, but it is worth understanding the rule, because it is the same rule whether you use a tool or do it on paper: pick one system and stay in it.

Where this one is handy

This is the general purpose member of the family. It suits physics and maths homework, where the question hands you two of the three and asks for the third in tidy units. It works for any moving thing, a runner, a cyclist, a train, a plane, not only road vehicles, which is why it carries the smaller units like meters and feet. If your question is specifically how long a drive will take, the drive time calculator is the simpler tool for that, and if you want an actual clock arrival time, the estimated time of arrival calculator adds your departure time and stops.

Questions people ask

What are the three formulas?

Speed equals distance divided by time, distance equals speed times time, and time equals distance divided by speed. They are the same relationship written three ways.

How do I know which one to calculate?

Pick the value you do not have. If you know how far and how fast but not how long, choose Find Time. If you know how far and how long but not how fast, choose Find Speed, and so on.

Can I mix units, like a distance in miles and a speed in km/h?

The tool will line them up for you, but on paper you should convert first so both sit in the same system. Speed has to be measured in the same distance and time units you are using, or the result is off.

Does this assume a constant speed?

Yes. It treats the speed as steady for the whole distance. If your speed varied and you want the overall figure for a real trip, the average speed calculator works that out from your total distance and total time.

References

1. National Institute of Standards and Technology (NIST), Special Publication 811: Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811
2. Bureau International des Poids et Mesures (BIPM), The International System of Units (SI Brochure, 9th edition). https://www.bipm.org/en/publications/si-brochure