What is the Moon's mass in Earth masses?

The Moon's mass is approximately 0.0123 Earth masses. In other words, the Moon contains about 1.23% of Earth's mass, or roughly one-eightieth as much material.

Using Earth's mass of about 5.9722 × 10²⁴ kilograms, the lunar value corresponds to approximately 7.35 × 10²² kilograms. Astronomers often express the figure as a ratio because comparing celestial masses in Earth or solar units is convenient and avoids unnecessary dependence on kilogram conversions.

The Moon's relatively small mass helps explain its weaker surface gravity. Although its mass is only 1.23% of Earth's, its radius is about 27.3% of Earth's. Surface gravity depends on both mass and radius, so lunar gravity is about 16.5% of Earth's—close to one-sixth, rather than 1.23%.

The Moon is thought to have formed after a giant impact early in Earth's history, leaving Earth and its satellite with a close compositional and dynamical relationship. Its mass also strongly affects tides, though the Sun contributes substantially as well. The nearby options are misleading: 0.01 is a rougher approximation, but 0.0123 is the standard rounded value used in planetary fact sheets.