How Many Miles Around the Earth? Circumference at the Equator and Poles

The Earth is 24,901 miles (40,075 km) around at the Equator. Measured through both poles it is 24,860 miles (40,008 km), about 42 miles (67 km) shorter. Both numbers come straight from the WGS84 ellipsoid, the model of Earth's shape behind GPS.

The difference exists because the Earth is not a perfect sphere. Its rotation makes it bulge at the Equator and flatten at the poles, so a cross-section through the poles is an ellipse rather than a circle. The Earth turns once every 23 hours 56 minutes relative to the stars, so a point on the Equator travels its 24,901 miles at about 1,040 mph. That spin pushes the equatorial belt outward; at the poles the ground only turns in place, so there is no bulge. The equatorial radius is 13.3 miles (21.4 km) longer than the polar radius. That flattening is only about 1 part in 298, so the ellipse looks like a perfect circle when drawn to scale; the figure exaggerates it 30 times.

When someone asks "how many miles around the Earth", the usual answer is the equatorial figure, 24,901 miles, often rounded to 25,000.

WGS84 defines the Earth's shape with two numbers: the equatorial radius a = 6,378,137 m and the flattening f = 1/298.257223563. Everything else follows.

1. Polar radius: b = a × (1 − f) = 6,356,752.3 m (3,949.9 mi).
2. Equatorial circumference: the Equator is a circle of radius a, so C = 2πa = 40,075,016.7 m, or 24,901.46 miles.
3. Meridional circumference: a meridian is half of an ellipse with semi-axes a and b. Its length has no simple closed formula; it is an elliptic integral. Integrating numerically gives a quarter meridian (Equator to pole) of 10,001,965.7 m, so the full pole-to-pole loop is 40,007,862.9 m, or 24,859.73 miles.

Two historical units fall out of the meridian length. The meter was originally defined in the 1790s as one ten-millionth of the distance from the North Pole to the Equator; the modern value of that distance, 10,001,966 m, shows the original survey was off by only about 0.02%. The nautical mile was based on one minute of latitude, so the full meridian is close to 360 × 60 = 21,600 nautical miles; with today's exact 1,852 m nautical mile it comes to 21,603.

If you use a single average radius instead (the mean radius of 6,371.0 km), 2πR gives 24,874 miles (40,030 km), which falls between the two true values and is fine for rough work.

The Equator is the longest parallel. Every other line of latitude is a smaller circle, and its length shrinks with the cosine of the latitude. Computed on the WGS84 ellipsoid:

So a trip "around the world" eastward along the 40th parallel is about 5,800 miles shorter than one along the Equator. The equator map shows where the 24,901-mile line runs: it crosses 13 countries, and about 21% of its length is on land.

The Earth's diameter is 7,926 miles (12,756 km) through the Equator and 7,900 miles (12,714 km) from pole to pole. Its radius ranges from 3,963 miles at the Equator to 3,950 miles at the poles, with a mean of 3,959 miles (6,371 km).

A few comparisons put those numbers in context:

• The surface area of the WGS84 ellipsoid is about 196.9 million square miles (510.1 million km²).
• The difference between the equatorial and polar radius, 13.3 miles, is larger than the height of Mount Everest above sea level (5.5 miles), which is why the summit farthest from Earth's center is not Everest but Chimborazo in Ecuador, close to the Equator.
• A tunnel straight through the center would be about 7,900 to 7,926 miles long, depending on where it starts. The map tunnel tool shows where you would come out; for most places on land, it is the ocean.

The point exactly opposite you, your antipode, is half a circumference away along the surface: between 12,430 miles (half a meridian) and 12,451 miles (half the Equator). The antipode finder computes it for any address.

The first known measurement of the Earth's circumference came from Eratosthenes, the librarian of Alexandria, around 240 BCE. As described by the American Physical Society:

1. At noon on the summer solstice, sunlight reached the bottom of a well in Syene (modern Aswan), so the Sun was directly overhead there.
2. At the same time in Alexandria, a vertical stick cast a shadow at about 7.2°, which is 1/50 of a full circle.
3. Because the Sun is so far away, its rays arrive essentially parallel. The 7.2° shadow angle therefore equals the angle between Syene and Alexandria measured at Earth's center.
4. The distance between the cities was taken as 5,000 stadia. If 5,000 stadia is 1/50 of the circle, the whole circle is 250,000 stadia.

How good was it? Nobody knows exactly how long his stadion was, so modern conversions of 250,000 stadia range from about 24,000 to 29,000 miles, which brackets the true 24,901. The method also rests on assumptions that are close but not exact: with modern coordinates Alexandria is 7.1° north of Aswan and about 3° west of it, and Aswan sits slightly north of the Tropic of Cancer. The geometry is still exactly right, and anyone can repeat it today with two sticks, two cities and a shared moment of local noon.

Traveling the 24,901 miles of the Equator nonstop at a steady speed would take:

Real trips take far longer: roads do not follow the Equator, about 79% of the Equator is ocean, and no one walks 24 hours a day. A realistic walking pace of 20 miles a day would need about 3.4 years for the same distance.

For actual journeys, the length of the route between two places matters more than the circumference. The distance between cities calculator gives the great-circle distance and an estimated flight time for any pair.

Because the Earth is round, the shortest route between two places follows a great circle (more precisely, a geodesic on the ellipsoid). On a flat map it often looks curved: the flight from New York to London bends north, and the flight from Los Angeles to Tokyo passes near Alaska. Tools on this site compute those distances with Karney's geodesic algorithm on the WGS84 ellipsoid, which is accurate to well under a millimeter at any distance.

Two quick rules of thumb follow from the circumference:

• One degree of latitude is about 1/360 of 24,860 miles, or 69 miles (111 km), anywhere on Earth.
• One degree of longitude is 69.2 miles at the Equator and shrinks with the cosine of latitude: 60 miles at 30°, 53 miles at 40°, 35 miles at 60°.

Those numbers are enough to sanity-check any distance calculation. If a tool reports a distance longer than about 12,450 miles between two points on the surface, something is wrong: no two places are farther apart than half the Equator.

The same radius decides how much of that curve you can see at once. Standing on a beach, the surface drops away so quickly that the sea disappears about 3 miles out; from an airliner the view reaches about 230 miles. The guide on how far the horizon is works through the geometry, which needs nothing more than the radius from the table above and the Pythagorean theorem.