Average Speed

How to calculate average speed, distance, and time using the speed-distance-time triangle.

The Formula

Average Speed

v = \dfrac{d}{t}

speed = distance ÷ time

Distance

d = v \cdot t

distance = speed × time

Time

t = \dfrac{d}{v}

time = distance ÷ speed

The Speed-Distance-Time Triangle

Units

Quantity	Common units
Speed	m/s, km/h
Distance	m, km
Time	s, h

Converting: 1 km/h = 1000 ÷ 3600 m/s ≈ 0.278 m/s

A car travels 180 km in 2 hours. Find its average speed.

$v = \dfrac{180}{2} = 90 \text{ km/h}$

How far does a runner travel in 45 seconds at 8 m/s?

$d = 8 \times 45 = 360 \text{ m}$

Real world: Road trip navigation

A family drives from London to Edinburgh, roughly 650 km. The journey takes 6.5 hours including a short rest stop. Their average speed for the whole trip:

$v = \dfrac{650}{6.5} = 100 \text{ km/h}$

They weren't doing exactly 100 km/h the whole time — average speed smooths out all the speeding up, slowing down, and stopping along the way.

Real world: Sprint athlete

Usain Bolt's 100 m world record took 9.58 s. His average speed over the race:

$v = \dfrac{100}{9.58} \approx 10.4 \text{ m/s} \approx 37.6 \text{ km/h}$

Real world: Cycling to school

A student cycles 6 km to school and arrives in 20 minutes (= 1/3 h). Their average speed:

$v = \dfrac{6}{1/3} = 18 \text{ km/h}$

Tip

Where do you see this in real life? GPS navigation apps constantly recalculate your average speed to estimate arrival time. Your car's speedometer shows instantaneous speed, but average speed tells you how long your whole journey will take.

Practice Problems

A cyclist covers 36 km at an average speed of 12 km/h. How long does the journey take?

Show answer

t = 36 ÷ 12 = 3 hours.

A train travels at 90 km/h for 1.5 hours. What distance does it cover?

Show answer

d = 90 × 1.5 = 135 km.