Space · Gravity
Planet surface gravity calculator.
Choose a world, or enter mass and radius, to see how strong gravity is at the surface.
Inputs
Surface gravity
Choose a body.
How surface gravity is calculated
Gravity at a body’s surface is g = GM / r², where GM is the body’s gravitational parameter and r is the distance from its centre. For a custom body the tool uses G = 6.6743 × 10-11 m³ kg-1 s-2 times the mass. For the presets it uses JPL’s DE440 GM values and NASA equatorial radii. One “g” is the standard 9.80665 m/s².
Worked example. Mars: GM = 42,828.4 km³/s², r = 3,396 km, so g = 42,828.4 / 3,396² = 0.003714 km/s² = 3.71 m/s², or 0.379 g. NASA lists 3.7 m/s². A 70 kg mass weighs about 26.5 kgf there against 70 kgf on Earth.
The calculation ignores rotation and shape, so it can differ from NASA’s listed values. For gas giants the radius is the 1 bar level; fast spin lowers effective gravity at the equator (Jupiter: 24.8 here, 23.1 listed by NASA). The Sun figure is gravity at the visible surface.
Frequently asked questions
What is the surface gravity of Mars?
About 3.71 m/s², or 0.38 g. NASA lists 3.7 m/s².
How do you calculate gravity on a planet?
Divide the planet’s gravitational parameter GM (or G times its mass) by the square of its radius.
Why does the result differ from the NASA value for Jupiter?
This tool gives pure GM/r². NASA’s listed gravity accounts for the planet’s fast rotation at the equator, which reduces it, so Jupiter reads 24.8 here and 23.1 there.
What is 1 g?
The standard acceleration of gravity, defined as exactly 9.80665 m/s². Earth’s surface value varies slightly with latitude and altitude.
Does gravity depend on the mass of the object on the surface?
No. The acceleration is the same for any object; only the weight force scales with mass.
Sources
Checked
- NASA JPL SSD: Astrodynamic Parameters (GM values, DE440)
- NASA NSSDCA: Planetary Fact Sheet (metric)
- NASA NSSDCA: Moon Fact Sheet
- NIST CODATA: standard acceleration of gravity
- NIST CODATA: Newtonian constant of gravitation
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Scope
Spherical-body estimate that ignores rotation. Not a substitute for measured values.