How to use this calculator
- Pick what to find, choose Speed, Distance or Time from the first menu. The field you are solving for is hidden, the other two stay on screen.
- Enter your two known values, type the numbers and choose a unit for each (km, miles or metres for distance, hours, minutes or seconds for time, km/h, mph or m/s for speed).
- Read the result, it updates as you type and is also shown in a couple of common units so you do not have to convert anything yourself.
Nothing is submitted or stored: the numbers never leave your device, so you can run as many calculations as you like privately.
The speed, distance, time formula
Speed, distance and time are tied together by one simple relationship, written three ways depending on what you need:
- Speed = distance ÷ time
- Distance = speed × time
- Time = distance ÷ speed
These are the same equation rearranged, so as soon as you know any two of the three values you can always find the third. The only thing to watch is units. Speed must use the same length and time units as the figures you feed in, which is why this tool converts everything to a common base (metres and seconds) before doing the maths, then converts the answer back for you.
Worked example
Suppose you drive 150 km and the journey takes 2 hours, and you want your average speed. Using speed = distance ÷ time, that is 150 ÷ 2 = 75 km/h, which is about 46.6 mph or roughly 20.8 m/s. Turn it around: if you know you can hold 75 km/h and you have 3 hours to drive, distance = speed × time = 75 × 3 = 225 km. And if you have 225 km to cover at 75 km/h, then time = distance ÷ speed = 225 ÷ 75 = 3 hours. The calculator does each of these for you and shows the answer in more than one unit.
A note on average speed
The speed this tool gives you is an average over the whole journey, total distance divided by total time. It does not capture how fast you were going at any single instant, and it assumes the distance and time you enter cover the same trip. Stops, traffic and changes in pace all get smoothed into the one figure, so treat the result as a planning aid rather than a record of your top speed.
Frequently asked questions
What is the formula for speed, distance and time?
Speed = distance ÷ time, distance = speed × time, and time = distance ÷ speed. They are rearrangements of the same relationship, so any two values give you the third.
How do I calculate average speed?
Divide the total distance by the total time. For example, 150 km in 2 hours is 75 km/h. It is an average, so it does not show your speed at any single moment.
How do I convert km/h to mph?
Multiply km/h by 0.621371 to get mph (so 100 km/h is about 62.1 mph). This calculator shows both at once, so you do not need to convert by hand.
Can I mix units like miles and km/h?
Yes. Each field has its own unit selector, so you can enter distance in miles, speed in km/h and time in minutes. Everything is converted to a common base first.
Is my data uploaded?
No, everything is calculated on your device and nothing is sent anywhere.