Whether you are planning a journey, checking a run, or solving a physics problem, knowing how to calculate average speed is a genuinely useful skill. The definition is simple and it never changes: average speed is the total distance you covered divided by the total time it took. The one thing that trips people up is that average speed is not the same as averaging your different speeds along the way. This guide gives you the formula, a clear worked example, the common units, and the important reason you cannot simply average two speeds. It also links speed to distance and time. To measure the distance for your calculation, our distance calculator is a handy tool.
Quick answer: To calculate average speed, divide the total distance travelled by the total time taken. If you drive 150 km in 2 hours, your average speed is 150 divided by 2, which is 75 km/h. This is total distance over total time, not the average of different speeds.
The average speed formula
Average speed = total distance / total time
Add up all the distance you travelled and all the time it took, including any stops if you want your overall average, then divide. The result is your average speed in distance per unit of time, such as kilometres per hour.
A worked example
Suppose you drive 150 kilometres and it takes 2 hours.
- Total distance: 150 km.
- Total time: 2 hours.
- Average speed: 150 / 2 = 75 km/h.
In plain English: covering 150 km in 2 hours means an average speed of 75 km/h, even if you actually drove faster on the motorway and slower in town. The average smooths all of that into one figure.
Measure your distance
You need the distance to calculate speed. Our distance calculator finds it between points or places, and our guide on calculating travel time rearranges the same formula to estimate how long a trip will take.
Common speed units
Average speed can be expressed in several units, depending on context:
| Unit | Used for |
|---|---|
| km/h (kilometres per hour) | driving in most countries |
| mph (miles per hour) | driving in the US and UK |
| m/s (metres per second) | science and physics |
Keep your distance and time units matched to the speed unit you want, kilometres and hours give km/h, metres and seconds give m/s.
Why you cannot just average speeds
Here is the classic mistake. If you drive one leg at 60 km/h and another at 100 km/h, your average speed is usually not 80 km/h. That simple average only works if you spend equal time at each speed, not equal distance.
Because you spend more time on the slower leg when the distances are equal, the true average is pulled below the midpoint. Always go back to the definition: add the total distance, add the total time, and divide. Do not average the speeds directly.
Finding distance or time
The same formula rearranges to find the other quantities:
- Distance = average speed x time.
- Time = distance / average speed.
So at 75 km/h, a 3-hour drive covers 225 km, and a 300 km trip takes 4 hours. These three versions of the speed-distance-time relationship cover almost every journey question.
Frequently asked questions
How do I calculate average speed?
Divide the total distance you travelled by the total time it took. If you cover 150 kilometres in 2 hours, your average speed is 150 divided by 2, which is 75 km/h. Make sure your distance and time units match the speed unit you want. Include stops in the time if you want your overall average.
What is the formula for average speed?
The formula is average speed equals total distance divided by total time. It rearranges to distance equals speed times time, and time equals distance divided by speed. These three forms let you find any one of speed, distance, or time when you know the other two, covering most journey calculations.
Why is average speed not the average of two speeds?
Because you usually spend different amounts of time at each speed. Averaging two speeds only works if the time spent at each is equal. Over equal distances, you spend more time at the slower speed, which pulls the true average below the simple midpoint. Always use total distance divided by total time instead.
How do I convert km/h to m/s?
Divide the speed in kilometres per hour by 3.6 to get metres per second, since there are 3,600 seconds in an hour and 1,000 metres in a kilometre. So 75 km/h is 75 divided by 3.6, which is about 20.8 m/s. To go the other way, multiply metres per second by 3.6.
Does average speed include stops?
It depends on what you are measuring. If you want your overall average speed for a journey, include the time spent stopped in the total time, which lowers the average. If you want your average moving speed, exclude stops. Be clear which you mean, as the two figures can differ significantly on a trip with breaks.
The bottom line
To calculate average speed, divide total distance by total time, so 150 km in 2 hours is 75 km/h. Keep your units matched, and remember the key trap: you cannot simply average two speeds unless the time at each is equal. The same formula rearranges to find distance or time. Measure your distance with our distance calculator and estimate journeys with our travel time guide.
Further reading
For authoritative background on this topic, see Speed on Wikipedia.
Note. This article is for general educational purposes.
Last reviewed: July 2026