Speed, distance, and time relationship
For motion at a constant average speed, distance, speed, and elapsed time are related by distance = speed × time. Rearranging gives speed = distance ÷ time and time = distance ÷ speed. This calculator lets you solve for one value when the other two are known.
Worked example
Travelling 100 km in 2 hours gives an average speed of 100 ÷ 2 = 50 km/h. At a constant 50 km/h, a 150 km trip would take 150 ÷ 50 = 3 hours, excluding stops or delays.
Average speed does not describe every speed change along a route. Check the units: distance in miles pairs naturally with mph, kilometers with km/h, and meters with m/s. The estimate cannot account for traffic, breaks, route changes, or acceleration and deceleration unless those effects are reflected in the average speed you enter.
Tips for accurate results
The three quantities are linked by distance = speed × time. Rearrange to find whichever one is missing, and keep the units consistent, such as kilometers with hours. A 150 km trip at 60 km/h takes 2.5 hours, or 2 hours 30 minutes.
Common mistakes and limits
Average speed is total distance divided by total time, not the average of two speeds. Driving 60 km at 60 km/h and then 60 km at 40 km/h takes 2.5 hours for 120 km, an average of 48 km/h rather than 50. Stops, traffic, and speed limits make real trips longer than the ideal figure.