What is average speed?

Moving through space and time

When a car, a cyclist, or a runner moves, it covers a certain distance over a certain time. Average speed measures the "pace" at which this movement happened, on average, over the whole trip.

The average speed formula

Average speed v is calculated as follows:

v = d / t

• d: distance covered
• t: duration of the trip
• v: average speed

Concrete example

A cyclist covers 30 km in 2 hours.

v = 30 / 2 = 15 km/h

This does not mean the cyclist was riding at 15 km/h the whole time: they may have gone faster downhill and slower uphill. Average speed "smooths out" all the variations of the trip.

Classic pitfall to avoid

Do not confuse adding and dividing speeds! If you ride at 10 km/h for the first half of the trip and 30 km/h for the second half, the average speed is NOT (10+30)/2 = 20 km/h, unless both parts last exactly the same amount of time. In general, you should always go back to the formula v = total distance / total time.

Trip	Distance	Time	Average speed
Walking	4 km	1 h	4 km/h
Cycling	30 km	2 h	15 km/h
Car	120 km	1.5 h	80 km/h