Planet Surface Gravity Calculator
A world's surface gravity, escape velocity and mean density from its mass and radius in Earth units — and what a person would weigh standing on it.
Surface gravity is GM over R squared: mass pulls, radius dilutes.
How the planet surface gravity calculator works
Surface gravity is GM over R squared: mass pulls, radius dilutes. Mars has a tenth of Earth's mass but half its radius, so its gravity is 0.107 / 0.532², or 38% of ours. Escape velocity is the square root of 2GM over R — the speed to leave without coming back.
Density tells you what a planet is made of: 5.5 g/cm³ is rock and iron, 1.3 is a gas giant, 0.7 is Saturn, which would float.
Formula: g = GM / R²; v_esc = √(2GM / R); ρ = M / (4/3 π R³)
Worked examples
| Inputs | Surface gravity (m/s²) | Note |
|---|---|---|
| Earth | 9.82 | 9.82 m/s², 11.2 km/s |
| Mars | 3.7125 | 38% of Earth |
| Jupiter | 25.9329 | 2.5 g, but light as water |
FAQFrequently asked questions
How is surface gravity calculated?
GM over R squared. Double the mass and gravity doubles; double the radius and it falls to a quarter. Mass and radius together are what matter, not size alone.
What is escape velocity?
The speed at which an object's kinetic energy equals the gravitational energy holding it — leave the surface that fast and you never fall back. 11.2 km/s on Earth, 2.4 on the Moon, 60 on Jupiter.
Why is Jupiter's gravity only 2.5 g?
Because it is enormous in radius as well as mass. 318 Earth masses in 11 Earth radii is 318 / 121 — about 2.6.
What does density tell me?
Composition. Rock and iron give 4,000 to 5,500 kg/m³, ice and rock 1,500 to 2,500, gas giants under 1,700. Saturn is 687 — less than water.
Where do I find a planet's mass and radius?
Any planetary fact sheet lists both in Earth units. For exoplanets, radius comes from transits and mass from radial velocity; when both exist, this page gives the density that classifies the world.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G and the speed of light
- IAU 2015 Resolution B3 — nominal solar and planetary conversion constants — the astronomical unit, solar mass and planetary radii
- Royal Observatory Greenwich — the historic home of the prime meridian
Last checked: September 2026. Constants are CODATA 2018 (G, c) and IAU 2015 nominal values (solar and planetary parameters).