Surface Gravity Calculator

How it is calculated

Instead of using the gravitational constant directly, the tool scales everything against Earth: g = (M ÷ R²) × 9.80665. Here M is the body's mass in Earth masses and R is its radius in Earth radii, both unitless multiples of Earth. Gravity falls with the square of the radius, so a body twice as wide with the same mass has a quarter of the pull. The tool shows g in m/s² with two decimals and also as a multiple of Earth's surface gravity with three decimals. Mass and radius must both be above zero. The result is the gravity at the surface of a non-rotating sphere and ignores spin, which lowers the effective pull near the equator.

Common mistakes

• Entering mass in kilograms or radius in kilometres. The fields use Earth units, so Earth itself is 1 and 1, and Mars is about 0.107 and 0.532.
• Entering the diameter instead of the radius. Doubling the radius cuts gravity to a quarter, so a diameter gives a result four times too low.
• Confusing mass and weight. The tool gives the acceleration at the surface; your mass stays the same on every body, only your weight changes.
• Applying it to gas giants as if it were solid ground. For a planet such as Jupiter the result is the pull at the cloud tops, not at a surface you can stand on.
• Treating the result as the pull inside the body or at some height above it. It holds only at the stated radius.