Earth, circling the Sun at an average distance of 93 million miles, is the fifth-largest planet and the third from the Sun. It orbits the Sun at a speed of 67,000 mph, making one revolution in 365 days, 5 hours, 48 minutes, and 45.51 seconds. Earth completes one rotation on its axis every 23 hours, 56 minutes, and 4.09 seconds. Actually a bit pear-shaped rather than a true sphere, Earth has a diameter of 7,927 mi at the equator and a few miles less at the poles. It has an estimated mass of about 6.6 sextillion tons, with an average density of 5.52 grams per cubic centimeter. Earth's surface area encompasses 196,949,970 sq mi of which about three-fourths is water.