Earth’s Circumference

The Earth’s circumference – the distance around the equator – is 40,075 kilometers around. That’s sounded nice and simple, but the question is actually more complicated than that. The circumference changes depending on where you measure it. The Earth’s meridional circumference is 40,008 km, and its average circumference is 40,041 km.

Why are there different numbers for the Earth’s circumference? It happens because the Earth is spinning. Think about what happens when you spin around holding a ball on a string. Your rotation creates a force that holds the ball out on the end of the string. And if the string broke, the ball would fly away. Even though the Earth is a solid ball of rock and metal, its rotation causes it to flatten out slightly, bulging at the equator.

That bulge isn’t very much, but when you subtract the meridional circumference (the equator when you pass through both poles), and the equatorial circumference, you see that it’s a difference of 67 km. In other words, if you drove your car around the equator of the Earth, you would drive an extra 67 km than you would if you drove from pole to pole to pole.

And that’s why the average circumference of Earth is 40,041 km. Which answer is correct? It depends on how accurate you want to be with your calculation.

We have written many articles about the Earth for Universe Today. Here’s an article about how fast the Earth rotates, and here’s an article about how round the Earth is.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Fraser Cain

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay. Here's a link to my Mastodon account.

Recent Posts

How Could Astronauts Call for Help from the Moon?

Exploring the Moon poses significant risks, with its extreme environment and hazardous terrain presenting numerous…

11 hours ago

There Was a 15 Minute Warning Before Tonga Volcano Exploded

Volcanoes are not restricted to the land, there are many undersea versions. One such undersea…

11 hours ago

Main Sequence and White Dwarf Binaries are Hiding in Plain Sight

Some binary stars are unusual. They contain a main sequence star like our Sun, while…

13 hours ago

What a Misplaced Meteorite Told Us About Mars

11 million years ago, Mars was a frigid, dry, dead world, just like it is…

15 hours ago

Uranus is Getting Colder and Now We Know Why

Uranus is an oddball among the Solar System's planets. While most planets' axis of rotation…

18 hours ago

How Scientists Repurposed a Camera on ESA’s Mars Express Mission

A camera aboard the Mars Express orbiter finds a new lease on life. Sometimes, limitations…

20 hours ago