Surface gravity calculator.

How surface gravity is worked out

Newton's law of gravitation gives the pull at a body's surface as g = G · M / r², where G = 6.6743 × 10⁻¹¹ m³ kg⁻¹ s⁻² (NIST CODATA), M is the mass and r the radius. The result is in metres per second squared; dividing by the standard gravity of 9.80665 m/s² expresses it in g. Because gravity falls with the square of distance, doubling a planet's radius at the same mass quarters its surface gravity.

Worked example. Earth's mass is 5.9722 × 10²⁴ kg and its volumetric mean radius is 6,371 km (NASA). The tool returns 9.82 m/s², which matches NASA's listed mean surface gravity of 9.820 m/s². Mars (0.64169 × 10²⁴ kg, radius 3,389.5 km) gives 3.73 m/s², NASA lists 3.73. For Jupiter and Saturn, NASA quotes gravity at the 1 bar pressure level, which is why the presets use their 1 bar values (25.92 and 11.19 m/s²).

Real surface gravity varies slightly with latitude because planets spin and bulge. NASA's Jupiter sheet, for example, gives 23.12 m/s² at the equator and 27.01 at the poles. This tool models a non-rotating sphere.