Average speed is the total distance traveled divided by the total time taken. If a car goes 150 miles in 3 hours, its average speed is 150 ÷ 3 = 50 miles per hour, even if it sped up and slowed down along the way. It is not the average of the separate speeds unless each speed lasted equally long.
Both legs are 60 miles, but the slow leg lasts twice as long. Total distance over total time gives 40 mph; averaging the two speeds gives the wrong 45 mph.
Formal definition and notation
For a trip of total distance d covered in total elapsed timet, with t > 0, the average speed is s̄ = dt. For a trip in parts, s̄ = d1 + d2 + ⋯t1 + t2 + ⋯. It is the constant speed that would cover the same distance in the same time, and it is a unit rate with units of distance per unit of time.
Average speed uses totals: add all distances, add all times, then divide once.
If two legs cover the same distance at different speeds, the average speed is lower than the plain mean of the two speeds, because the slow leg takes longer.
If two legs last the same time, the average speed does equal the mean of the two speeds.
Stops count: a 20-minute break adds time but no distance, so it lowers the average speed.
The mean of the speeds adds the speed values and divides by how many there are. Average speed divides total distance by total time. They match only when every speed lasts the same amount of time.
Average Speedvs.Average velocity
Average velocity uses displacement (start to finish, with direction). A 6 km round trip in 30 minutes has an average speed of 12 km/h but an average velocity of 0, because you end where you started.
A unit rate is any rate per 1 unit (dollars per pound, words per minute). Average speed is one unit rate: distance per 1 unit of time.
Quick check: 3 questions
Question 1 of 3
A cyclist rides 48 miles in 3 hours. What is the average speed?
Show answer and explanation
Answer: A.48 ÷ 3 = 16 mph. 144 multiplies instead of dividing, 51 adds, and 0.0625 divides time by distance.
Question 2 of 3
A car drives 100 miles at 50 mph and then 100 miles at 25 mph. What is its average speed for the 200 miles?
Show answer and explanation
Answer: C. Times: 100 ÷ 50 = 2 h and 100 ÷ 25 = 4 h. 200 ÷ 6 ≈ 33.3 mph. 37.5 is the mean of the speeds, 40 forgets one leg time, and 75 adds the speeds.
Question 3 of 3
A bus travels 12 km in 15 minutes. What is its average speed in km/h?
Show answer and explanation
Answer: D. 15 minutes is 0.25 hour, so 12 ÷ 0.25 = 48 km/h. 0.8 is km per minute, 12 ignores the time, and 180 multiplies 12 by 15.
Average Speed: frequently asked questions
Is average speed the average of the speeds?
Usually not. Average speed is total distance divided by total time. If you drive the same distance at 30 mph and at 60 mph, the slow part takes twice as long, so the average speed is 40 mph, not 45. The plain mean of the speeds works only when you spend the same time at each speed.
How do you find average speed with minutes?
Change the minutes into hours before dividing, by dividing the minutes by 60. For 18 miles in 24 minutes, 24 minutes is 0.4 hour, and 18 ÷ 0.4 = 45 mph. Or find the speed per minute first, 18 ÷ 24 = 0.75 mile per minute, and multiply by 60 to get 45 mph.
Is average speed a unit rate?
Yes. Average speed tells you the distance covered per 1 unit of time, such as miles per hour or meters per second, so it is a unit rate. That is why it appears in the grade 6 ratio standards next to unit pricing, and why its units always read distance per time.
Updated November 2026·Reviewed by the Effortless Math team·Standards: CCSS 6.RP.A.3.b
Cite this entry
Effortless Math Team. “Average Speed.” Effortless Math Dictionary. Updated November 2026. https://www.effortlessmath.com/math-dictionary/average-speed/
Flashcard
TermAverage Speedtotal distancetotal time
DefinitionTotal distance divided by total time. 60 miles at 60 mph plus 60 miles at 30 mph: 120 ÷ 3 = 40 mph, not 45.
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