query: What is the circumference of the planet Earth?
passage: Earth's circumference
Earth's circumference is the distance around the Earth, either around the equator (40,075.017km [24,901.461mi][1]) or around the poles (40,007.86km [24,859.73mi][2]).
passage: Great-circle distance
The shape of the Earth closely resembles a flattened sphere (a spheroid) with equatorial radius formula_17 of 6378.137 km; distance formula_18 from the center of the spheroid to each pole is 6356.752 km. When calculating the length of a short north-south line at the equator, the circle that best approximates that line has a radius of formula_19 (which equals the meridian's semi-latus rectum), or 6335.439 km, while the spheroid at the poles is best approximated by a sphere of radius formula_20, or 6399.594 km, a 1% difference. So long as a spherical Earth is assumed, any single formula for distance on the Earth is only guaranteed correct within 0.5% (though better accuracy is possible if the formula is only intended to apply to a limited area). Using the mean earth radius, formula_21 (for the WGS84 ellipsoid) means that in the limit of small flattening, the mean square relative error in the estimates for distance is minimized.