Earth, which is almost round in shape, measures 24,901 miles (39,842 kilometers) around at its widest part, the equator. (The equator is the imaginary line that crosses the planet midway between the North and South Poles.) A measurement through Earth at the equator in other words, the planet’s diameter reveals that it is 7,926 miles (about 12,700 kilometers) across. Earth’s weight, or mass (the amount of matter it is made of), is around 6 sextillion tons. That is 6 with 21 zeros after it! Because Earth cannot be put on an enormous scale to find its weight, scientists use the laws of gravity and mathematical equations to figure this out.