Planetary Surface Gravity Calculator
Surface gravity is the acceleration that a falling object experiences at the surface of a planet or moon. Newton's law of gravitation gives it directly from the body's mass and radius: gravity equals the gravitational constant times the mass divided by the radius squared. This calculator uses the CODATA value of the gravitational constant and returns the surface gravity in meters per second squared, as a multiple of Earth's gravity, and the corresponding weight of a reference mass. Enter the mass and radius from NASA's planetary fact sheet for any body you like; both are user-editable.
Surface gravity formula
g = G * M / r^2
G = 6.67430e-11 m^3 kg^-1 s^-2 (CODATA)
relative = g / 9.80665
weight = reference mass * g
escape velocity = sqrt(2 * G * M / r)
Mass in kilograms and radius in meters give gravity in meters per second squared. The escape velocity is the speed needed to leave the body's gravity from the surface, reported here in kilometers per second.
Surface gravity notes
- The default inputs are Earth's mass and mean radius.
- Earth's standard surface gravity is 9.80665 meters per second squared.
- Use NASA's planetary fact sheet for the mass and radius of other bodies.
- Scientific notation like 5.972e24 is accepted in the inputs.
- Rotation and equatorial bulge are not modeled; this is the spherical-body value.
Surface gravity: frequently asked questions
How is surface gravity calculated from mass and radius?
Surface gravity g equals the gravitational constant G times the body's mass M divided by the square of its radius r. With M in kilograms and r in meters, g comes out in meters per second squared. The gravitational constant is a fixed value of about 6.674 times ten to the minus eleven.
What value of G does this use?
It uses the CODATA recommended Newtonian constant of gravitation, 6.67430 times ten to the minus eleven cubic meters per kilogram per second squared, the value published by NIST. The constant is fixed in the calculation; you enter the body's mass and radius.
Where do I find a planet's mass and radius?
NASA's planetary fact sheet lists mass and mean radius for every planet and major moon. The calculator's inputs are user-editable so you can enter the published figures for any body, including bodies discovered after this page was written.
How does the result compare to Earth gravity?
The calculator also reports the result as a multiple of Earth's surface gravity of 9.80665 meters per second squared. A value of 0.38 means the surface gravity is 38 percent of Earth's, which is about right for Mars.
Does this account for rotation or non-spherical shape?
No. It gives the gravitational acceleration for a spherical body of the stated mass and radius. Rapid rotation and equatorial bulge slightly reduce the effective weight at the equator, but that refinement is not included in this idealized calculation.
Official sources
- NASA NSSDCA: planetary fact sheet (mass and radius).
- NIST: Newtonian constant of gravitation.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.