Surface gravity comes from mass and radius
A planet's surface gravity g is set by how much mass it has and how far its surface sits from the center. More mass pulls harder; a bigger radius spreads that pull out. This is why tiny, dense worlds and huge, puffy ones can land in surprising places.
G is the gravitational constant (6.674 × 10−11), M is the planet's mass and R its radius. On Earth this gives the familiar 9.81 m/s².
Surface gravity across the solar system
| Body | g (m/s²) | vs Earth | 70 kg weighs |
|---|---|---|---|
| Mercury | 3.70 | 0.38× | 58 lb |
| Venus | 8.87 | 0.90× | 139 lb |
| Earth | 9.81 | 1.00× | 154 lb |
| Moon | 1.62 | 0.17× | 25 lb |
| Mars | 3.71 | 0.38× | 58 lb |
| Jupiter | 24.79 | 2.53× | 388 lb |
| Saturn | 10.44 | 1.06× | 164 lb |
| Uranus | 8.69 | 0.89× | 136 lb |
| Neptune | 11.15 | 1.14× | 175 lb |
Gas-giant figures are for the cloud tops, since these worlds have no solid surface to stand on. The Moon is included because it is where most people picture reduced gravity.
The same person, three worlds
A 70 kg body reads 25 lb on the Moon and 388 lb at Jupiter — a 15-fold swing — while its mass never changes.
Two things that shift g on Earth itself
- Latitude. Earth's spin and its slight bulge make g about 9.780 at the equator and 9.832 at the poles — a real, if small, difference.
- Altitude. g falls with height, roughly 0.003 m/s² per 100 m. On the ISS at 400 km it is still about 8.7 m/s²; astronauts float because they are in free fall, not because gravity is gone.
Common questions
Would I weigh more on Jupiter?
Yes, about 2.5 times more. Jupiter's surface gravity is 24.79 m/s2 against Earth's 9.81, so a 70 kg person who weighs 154 lb on Earth would register about 388 lb at Jupiter's cloud tops. Their mass in kilograms would not change.
Why is gravity on Mars only about a third of Earth's?
Surface gravity depends on a planet's mass and its radius. Mars has roughly a tenth of Earth's mass, and even though it is smaller, the mass shortfall wins out, leaving g at 3.71 m/s2 — about 38% of Earth's.
Does my mass or my weight change on another planet?
Only weight changes. Mass is the amount of matter in you and stays the same everywhere, so a scale reading in kilograms is really measuring weight and would mislead you off Earth. Weight is mass times the local g, and g is what differs from world to world.
