Earth Radius Converter

6,371 kilometres — on average

The Earth's mean radius is 6,371 km, or 6,371,000 metres. That single figure hides something important: the planet is not a sphere.

mean radius = 6,371,000 m = 6,371 km = 3,959 miles

Rotation makes it bulge at the equator and flatten at the poles:

• Equatorial radius — 6,378.1 km
• Polar radius — 6,356.8 km
• Mean radius — 6,371.0 km, the figure adopted by the International Union of Geodesy and Geophysics and used here

The difference is 21 km, about a third of a per cent. That sounds small and matters enormously: it is why satellite orbits precess, why GPS needs a reference ellipsoid rather than a sphere, and why the summit of Chimborazo in Ecuador is further from the Earth's centre than Everest despite being 2,500 m shorter.

The Earth radius is used as a unit in its own right in astronomy, written R_⊕. An exoplanet of 1.5 R_⊕ is half again as wide as our planet.

The Earth radius

The Earth is not a sphere. It bulges at the equator, where the radius is 6,378 km, and is flattened at the poles, where it is 6,357 km. The mean radius used here is 6,371 km, the figure adopted by the International Union of Geodesy and Geophysics.

It is used as a unit in astronomy and planetary science, where expressing a planet's size as a multiple of Earth's is more meaningful than quoting millions of metres.

The metre

The SI base unit of length. It began in 1793 as one ten-millionth of the distance from the equator to the North Pole, then became a platinum bar, and since 1983 has been defined by the speed of light: the distance light travels in 1/299,792,458 of a second.

That definition makes the metre exact and reproducible anywhere, which is why every other unit on this page is now defined in terms of it — including the foot and the inch.

The working, step by step

Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.

Copy the working

The same quantity, two different numbers

One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.

Your turn

Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.

How to use this converter

1. Type into either box. The other side updates as you go; there is no button to press.
2. Swap the direction with the button between the boxes, carrying your value across.
3. Set the decimals if the default is more or less precision than you need.
4. Copy the answer with its unit, ready to paste.
5. Use the shortcut buttons for the values that come up most often.
6. Share the result. The address bar tracks what you type, so the link you copy opens on the same number.

Common uses and tips

Where length conversions come up

• Height. Quoted in feet and inches in Britain and America, and in centimetres nearly everywhere else. 5 ft 10 in is 178 cm.
• Buying things online from another market, where the dimensions are in units your tape measure does not have.
• DIY and building, where materials come in metric sizes and older plans are in imperial.
• Screens, tyres and pipes, which stay in inches worldwide even in fully metric countries.
• Running and cycling, where race distances are metric and training apps may report either.

Numbers worth carrying

• 1 inch = 2.54 cm exactly. Everything imperial in this family descends from it.
• 1 foot = 30.48 cm, twelve inches.
• 1 yard = 0.9144 m, a little shorter than a metre.
• 1 mile = 1.609 km, and 1 km = 0.621 mile.
• A metre is about 39.37 inches, or 3 ft 3 in.

Mental shortcuts

Kilometres to miles: multiply by six and drop the last digit. 80 km × 6 = 480, drop the digit for 48 miles, against a true 49.7.

Miles to kilometres: add sixty per cent. 50 miles plus 60 % is 80 km, against a true 80.5.

Centimetres to inches: divide by 2.5 and take off a little. Dividing by 2.5 gives an answer about 1.6 % high.

Mistakes worth avoiding

• Feet and inches are not decimal. 5.5 feet is 5 ft 6 in, not 5 ft 5 in. Multiply the decimal part by twelve.
• Do not use length factors for area or volume. A foot is 0.3048 m, but a square foot is 0.0929 m² and a cubic foot 0.0283 m³.
• Check which mile. A nautical mile is 1,852 m, about 15 % longer than a statute mile.

Values people look up most

Each one opens the converter with the number already in it.

• 0.1 R⊕ to m
• 0.25 R⊕ to m
• 0.5 R⊕ to m
• 0.75 R⊕ to m
• 1 R⊕ to m
• 1.5 R⊕ to m
• 2 R⊕ to m
• 3 R⊕ to m
• 4 R⊕ to m
• 11 R⊕ to m
• 109 R⊕ to m

Quick reference

Jupiter is about 11 Earth radii; the Sun about 109.

Earth radii	Metres
0.25 R⊕	1,592,750 m
0.5 R⊕	3,185,500 m
1 R⊕	6,371,000 m
1.5 R⊕	9,556,500 m
2 R⊕	12,742,000 m
11 R⊕	70,081,000 m
109 R⊕	694,439,000 m

Questions people ask

What is the radius of the Earth in metres?

The mean radius is 6,371,000 m. The equatorial radius is 6,378,100 m and the polar radius 6,356,800 m.

Why are there three figures?

Because the Earth bulges at the equator. Which radius you want depends on what you are calculating.

What is the Earth's radius in miles?

About 3,959 miles on the mean radius.

What is the Earth's circumference?

About 40,075 km around the equator, and 40,008 km through the poles.