Speed calculator
Speed, distance or travel time: enter two to get the third.
About this calculator
This speed calculator solves the speed, distance and time triangle. Enter any two and it works out the third, in the units you choose.
Use it for road trips, flights, runs and rides, or for physics homework.
How it works
Speed = distance ÷ time, distance = speed × time, and time = distance ÷ speed. Everything is converted to metres and seconds first, so you can mix units.
Last reviewed:
Worked example
- Work out: Speed
- Distance: 120
- Distance in: Miles
- Hours: 2
Average speed: 60 mph
Common questions
How do I calculate average speed?
Divide the total distance by the total time. 150 km in 2 hours is an average of 75 km/h, even if you stopped along the way.
How do I convert km/h to mph?
Divide by 1.609. So 100 km/h is about 62 mph.
What is a knot?
One nautical mile per hour, about 1.852 km/h or 1.15 mph. It's used at sea and in aviation.
The story behind it
Where the idea came from: In 1865, the UK's Locomotive Act limited self-propelled road vehicles to 2 mph in towns, with a person walking ahead carrying a red flag.
The Red Flag Act shows how new speed felt to people in the 1800s. Today speed, distance and time are the first sums in any journey plan, from a school run to a transatlantic flight.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
Meet the founder