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Surface Gravity Calculator

Find the surface gravity of any planet relative to Earth.

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.

Worked example

Mars has about 0.107 Earth masses and 0.532 Earth radii. Radius squared: 0.532² = 0.283. Mass divided by that: 0.107 ÷ 0.283 = 0.378 of Earth's pull. Times 9.80665 gives about 3.71 m/s², shown as 3.71 m/s², and the tool also shows 0.378 g. A 70 kg person would weigh like about 26 kg on Earth.

Try this example →

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.

About this calculator

This calculator computes a planet or body's surface gravity from g = GM/r², then expresses it relative to Earth's 9.8 m/s² so the result reads as a simple multiplier like 0.38g for Mars or 2.5g for Jupiter.

Astronomy students, sci-fi writers, and space enthusiasts use it to compare how heavy an object — or a person — would feel on another planet, moon, or exoplanet given its mass and radius. Surface gravity is reported both in m/s² and in Earth-relative units.

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Comments (1)

  • Editorial team

    For gas giants there is no solid surface, so the radius you enter decides what the answer means. Astronomers usually quote the radius at the 1 bar pressure level. With about 317.8 Earth masses and 11.2 Earth radii for Jupiter, the tool gives roughly 2.5 g, but a different reference radius would shift it. The result also ignores rotation. Which planet, moon or exoplanet are you checking, and where did you get its mass and radius?

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