Skip to content

How big is the Earth?

Space and time · level 2, lesson 1 of 6

A question to start

If you could drive a car all the way round the Earth, without stopping, how long would it take?

The idea

The Earth is a huge ball. It is about 12,756 km across, through the middle. All the way round, it is about 40,000 km.

Driving at 100 km an hour, a car covers 100 km each hour. To go 40,000 km would take 400 hours. That is about 17 days, driving day and night without a single stop.

Mars is a smaller ball: about 6,792 km across, roughly half as wide as the Earth.

Size Mars Earth
Across the middle 6,792 km 12,756 km
All the way round about 21,300 km about 40,000 km
12,756 kmMars: 6,792 km

Worked examples

1. Round the Earth. 40,000 km at 100 km an hour: 400 hours. 400 hours is about 17 days.

2. Round Mars. About 21,300 km at 100 km an hour: 213 hours, about 9 days.

3. Half as wide. 6,792 is close to half of 12,756, so Mars is about half as wide as the Earth.

Try it

  1. About how wide is the Earth?
  2. About how far is it all the way round the Earth?
  3. Which is bigger, Earth or Mars?
  4. A plane flies at about 800 km an hour. About how long would it take to fly 40,000 km?
Answers
  1. About 12,756 km.
  2. About 40,000 km.
  3. The Earth.
  4. 50 hours: about 2 days.

Common mistake

"Mars is the same size as Earth." Mars is only about half as wide. It would take about seven Mars-sized balls to fill the space of the Earth.

Where it leads