Acceleration due to Gravity Calculator

Find the surface gravity g = GM/r2 of any planet, moon, or custom body from its mass and radius via Newton's law, plus the ratio to Earth gravity. Free.

Frequently Asked Questions

What is the formula for surface gravity?

g = G·M / r², where G = 6.674e-11 N·m²/kg², M is the body's mass, and r its radius.

What is Earth's gravity?

About 9.81 m/s² at sea level. It varies slightly with latitude (poles vs equator) and altitude.

How much gravity is on Mars or the Moon?

Mars: ~3.73 m/s² (0.38 g). Moon: ~1.62 m/s² (0.17 g). Both lighter because of smaller mass.

Why does the tool show Mars as ~3.73 m/s² when textbooks say 3.71?

The presets use each body's mean radius, while many references quote gravity at the equatorial radius. Mars is slightly oblate, so its equatorial radius is larger and yields a marginally lower g (~3.71). The ~0.5% difference is expected and simply reflects which radius is used, not an error.

How do I calculate my weight on another planet?

Your mass never changes, but your weight (W = m·g) scales with local gravity. Multiply your Earth weight by the ratio of that world's g to Earth's g. A person weighing 70 kg-force (about 686 N) on Earth would register roughly 0.38 of that on Mars (about 26.6 kg-force) and about 0.17 on the Moon (about 11.9 kg-force). So mass is the same everywhere; only weight goes up or down with g.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.