Direct answer: Average speed is total distance divided by total time: Average Speed = Distance ÷ Time. Drive 60 miles in 1.5 hours and your average speed is 40 mph, because 60 ÷ 1.5 = 40. The formula works for any units — miles per hour, kilometers per hour, or meters per second — as long as distance and time use matching units.
Average speed is the most practical average most students ever calculate: every road trip, every race, every “how long will it take?” question runs on this one formula. It is also the average most often calculated wrong, because of one trap: averaging two speeds directly gives the wrong answer whenever the times are different. This guide shows you the formula, four worked examples, and the two-speed trap — with exact numbers throughout. If you need the basics first, start with our guide on how to find the average.
The Average Speed Formula
Average Speed = Total Distance ÷ Total Time
Two words in that formula do all the work: total distance and total time. You add up every mile and every minute of the whole trip — including stops — and then divide once. That is the entire method:
- Find the total distance traveled (add up every leg of the trip).
- Find the total time taken (add up every leg, including stops and slow sections).
- Divide distance by time. The result is the average speed.
The units tell you what you are calculating: miles ÷ hours = miles per hour (mph); kilometers ÷ hours = km/h; meters ÷ seconds = m/s.
Worked Example: 60 Miles in 1.5 Hours = 40 mph
Step 1 — Distance: 60 miles.
Step 2 — Time: 1.5 hours.
Step 3 — Divide: 60 ÷ 1.5 = 40 mph.
The average speed is 40 mph.
A common stumble: 1.5 hours is 1 hour and 30 minutes, not 1 hour and 50 minutes. In decimal form, 30 minutes is 0.5 hours. Dividing 60 by 1.5 gives 40 — and a quick sanity check confirms it: at 40 mph for 1.5 hours you cover 40 × 1.5 = 60 miles. The numbers check out.
Worked Example: 120 Miles in 2 Hours
Step 1 — Distance: 120 miles.
Step 2 — Time: 2 hours.
Step 3 — Divide: 120 ÷ 2 = 60 mph.
The average speed is 60 mph.
And in metric: drive 300 kilometers in 4 hours and the average speed is 300 ÷ 4 = 75 km/h. Same formula, different units. You can check any of these instantly with Calcrio’s free average speed tool — the same average formula, applied to distance and time.
The Two-Speed Trap: Why You Cannot Average the Speeds
Here is the mistake almost everyone makes. A car drives at 60 mph for 1 hour, then at 30 mph for 2 hours. What is the average speed?
The wrong way: (60 + 30) ÷ 2 = 45 mph. This is the plain average of the two speeds — and it is wrong, because the car spent twice as long at 30 mph as at 60 mph.
The right way — total distance over total time:
| Leg | Speed | Time | Distance |
|---|---|---|---|
| 1 | 60 mph | 1 hour | 60 × 1 = 60 miles |
| 2 | 30 mph | 2 hours | 30 × 2 = 60 miles |
| Total | — | 3 hours | 120 miles |
Average speed = 120 ÷ 3 = 40 mph — not 45.
The car spent two-thirds of its time at the slower speed, so the true average sits closer to 30 than to 60. Averaging the speeds directly ignores how long each speed lasted. This is the same idea as a weighted average: the weights are the times, and the longer leg counts more.
The equal-distance shortcut: when the two halves of a trip cover the same distance at speeds a and b, the average speed is 2ab ÷ (a + b). Drive one half at 20 km/h and the other at 60 km/h: 2 × 20 × 60 ÷ (20 + 60) = 2,400 ÷ 80 = 30 km/h — not the plain average of 40. The slow half takes three times longer (the car covers the same distance at one-third the speed), so the average is pulled down toward 20. A second check: Sam covers 200 km in 4 hours, then 160 km in 4 hours — total 360 km ÷ 8 hours = 45 km/h. Equal times, so here the average of the speeds (50 and 40 km/h) would also give 45 — the only case where averaging speeds works.
Worked Example: The Round Trip
A car drives 60 miles out at 30 mph, then 60 miles back at 60 mph. Same distance each way — so the average speed must be 45 mph, right?
Wrong. Work it out with total distance over total time:
- Out: 60 miles ÷ 30 mph = 2 hours.
- Back: 60 miles ÷ 60 mph = 1 hour.
- Total distance: 60 + 60 = 120 miles.
- Total time: 2 + 1 = 3 hours.
- Average speed: 120 ÷ 3 = 40 mph.
The trip took longer at the slow speed, so the average is pulled down toward 30. The plain average of the speeds (45 mph) would only be correct if the car spent equal time at each speed — here it spent equal distance, which is a different thing. This round-trip problem is a favorite of exam writers precisely because the obvious answer is wrong.
Average Speed vs Instantaneous Speed
| Average speed | Instantaneous speed | |
|---|---|---|
| What it measures | The whole trip, start to finish | One moment in time |
| Formula | Total distance ÷ total time | What the speedometer shows right now |
| Example | 40 mph over a 3-hour trip | 55 mph at the moment you pass a sign |
A car can hit 70 mph on the highway and still average 40 mph for the trip, because traffic lights, towns, and fuel stops all count in the total time. Average speed describes the journey; instantaneous speed describes a moment.
Units: mph, km/h, and m/s
| Units | Used for | Conversion |
|---|---|---|
| mph (miles per hour) | Driving in the US | 1 mph ≈ 1.609 km/h |
| km/h (kilometers per hour) | Driving almost everywhere else | 1 km/h ≈ 0.621 mph |
| m/s (meters per second) | Physics problems, running | 1 m/s = 3.6 km/h |
A quick conversion example: 40 mph × 1.609 ≈ 64.4 km/h. And a sprinter running 100 meters in 10 seconds averages 100 ÷ 10 = 10 m/s, which is 36 km/h. Keep the units consistent — never divide miles by minutes without converting first — and the formula does the rest.
3 Common Mistakes with Average Speed
Mistake 1: Averaging the speeds directly. Two speeds only average to their midpoint when the times are equal. Use total distance ÷ total time instead.
Mistake 2: Forgetting stops in the total time. A 2-hour drive with a 30-minute stop is 2.5 hours of total time, not 2. Average speed counts every minute of the trip.
Mistake 3: Mixing up distance and time. Speed is distance divided by time. Dividing time by distance gives hours per mile — a real quantity (pace), but not speed.
Check Your Work with Calcrio’s Free Tool
The free tool at Calcrio calculates averages of any numbers — including speeds, distances, and times. Enter your values and it returns the average with the sum, count, minimum, maximum, and range. It is free, with no sign-up — and the fastest way to check an average-speed answer before it goes on a homework sheet. For the underlying method, see our guide on how to calculate average and the comparison of average vs median vs mode for when a different “average” fits better.
Frequently Asked Questions
What is the formula for average speed?
Average speed = total distance ÷ total time. Drive 60 miles in 1.5 hours and the average speed is 60 ÷ 1.5 = 40 mph.
How do you calculate average speed with two different speeds?
Do not average the speeds. Calculate the distance for each leg (speed × time), add the distances, add the times, and divide total distance by total time. At 60 mph for 1 hour and 30 mph for 2 hours: 120 miles ÷ 3 hours = 40 mph.
What is the average speed of 120 miles in 2 hours?
120 ÷ 2 = 60 mph. The average speed is 60 miles per hour.
Is average speed the same as speed?
No. Average speed describes a whole trip (total distance ÷ total time). Instantaneous speed is the speed at one moment — what the speedometer shows. A car can hit 70 mph and still average 40 mph for the trip.
What is the difference between average speed and average velocity?
Average speed uses total distance (the path traveled). Average velocity uses displacement (the straight-line distance from start to finish) and has a direction. On a round trip, the average velocity is zero — you end where you started — but the average speed is not.
Can average speed be zero?
Only if the total distance is zero — that is, if nothing moved. If you traveled at all, the average speed is positive, even if you returned to your starting point.