About this calculator
Speed, distance and time are tied together by one simple relationship. Fill in any two and this calculator finds the third, converting between kilometres, miles and metres, and between hours, minutes and seconds as needed.
The unit you choose for the box you leave empty is the unit of your answer, and the working shows the conversion.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
100 km in 2 hours: what speed?
- Speed
- 50 km/h
- In mph
- 31.069 mph
- In m/s
- 13.889 m/s
100 km in 2 hours is a speed of 50 km/h.
Show the working
- Speed = distance ÷ time.
- Convert to metres and seconds: 100,000 m ÷ 7,200 s = 13.889 m/s.
- Show it in km/h: 50.
60 mph for 30 minutes: how far?
- Distance
- 30 miles
- In kilometres
- 48.28 km
- In metres
- 48,280 m
Travelling at 60 mph for 30 minutes covers 30 miles.
Show the working
- Distance = speed × time.
- Convert to metres per second and seconds: 26.822 m/s × 1,800 s = 48,280 m.
- Show it in miles: 30.
A marathon (26.2 miles) in 4 hours: what speed?
- Speed
- 6.55 mph
- In km/h
- 10.541 km/h
- In m/s
- 2.9281 m/s
26.2 miles in 4 hours is a speed of 6.55 mph.
Show the working
- Speed = distance ÷ time.
- Convert to metres and seconds: 42,165 m ÷ 14,400 s = 2.9281 m/s.
- Show it in mph: 6.55.
90 km at 60 km/h: how long?
- Time
- 1.5 hours
- As hours, minutes and seconds
- 1 h 30 min 0 s
Covering 90 km at 60 km/h takes 1.5 hours.
Show the working
- Time = distance ÷ speed.
- Convert to metres and metres per second: 90,000 m ÷ 16.667 m/s = 5,400 s.
- Show it in hours: 1.5.
The formulas
Speed = distance ÷ time, distance = speed × time and time = distance ÷ speed. They're one relationship written three ways, so remember one and you can rearrange it for the others. At 50 km/h for 2 hours you travel 100 km.
The one rule is that the units must match. If the speed is in miles per hour, the time must be in hours before you multiply. This calculator converts everything to metres and seconds behind the scenes, so you can mix units freely.
Handy conversions
| To convert | Do this |
|---|---|
| km/h to m/s | divide by 3.6 |
| m/s to km/h | multiply by 3.6 |
| miles to km | multiply by 1.609344 |
| mph to km/h | multiply by 1.609344 |
| minutes to hours | divide by 60 |
Average speed, not instant speed
The answer is an average. A journey of 100 km in 2 hours is an average of 50 km/h even if you were sometimes going faster and sometimes stopped. Average speed over a whole trip is total distance divided by total time, not the average of the speeds. If you drive the first half of a route at 30 km/h and the second half at 60 km/h, your average is 40 km/h, not 45.
Frequently asked questions
How do I calculate speed?
Divide the distance by the time. 100 km in 2 hours is 100 ÷ 2 = 50 km/h.
How do I calculate how long a journey takes?
Divide the distance by the speed. 90 km at 60 km/h takes 1.5 hours, which is 1 hour 30 minutes.
How do I calculate distance?
Multiply the speed by the time, making sure the units match. 60 mph for half an hour is 30 miles.
How do I convert km/h to m/s?
Divide by 3.6. So 72 km/h is 20 m/s.
Why must I fill in only two boxes?
Two of the three values fix the third. If all three were filled in they might not agree, so clear the one you want to find.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.