The moon has a mass of 7.34 times 10^22 kilograms. The Earth has a mass of 5.98 times 10^24 kilograms, which makes the moon 81 times less massive than the Earth.
The moon is so much less massive than the Earth because its composition is different. The Earth has an average density of 5.5 grams per cubic centimeter, while the moon has a density of 3.3 grams per cubic centimeter. This explains why the moon can have a diameter of 27 percent of Earth and a mass of just 1.2 percent. Most of the difference is due to the lack of iron in the moon.