Planet Gravity Calculator Formula

Understand the math behind the planet gravity calculator. Each variable explained with a worked example.

Use the Planet Gravity Calculator

Formulas Used

Surface Gravity

gravity_ms2 = 9.80665 * mass_ratio / pow(radius_ratio, 2)

In Earth g

gravity_g = mass_ratio / pow(radius_ratio, 2)

Variables

VariableDescriptionDefault
mass_ratioMass (Earth masses)(M_E)1
radius_ratioRadius (Earth radii)(R_E)1

How It Works

Planet Surface Gravity

Ratio Formula

g / g_Earth = (M / M_Earth) / (R / R_Earth)²

This avoids needing G and absolute values. Just enter the planet's mass and radius relative to Earth.

Examples: Mars ≈ 0.38 g, Jupiter ≈ 2.53 g, Moon ≈ 0.17 g.

Worked Example

Mars: 0.107 Earth masses, 0.532 Earth radii.

mass_ratio = 0.107radius_ratio = 0.532
  1. 01g/g_E = 0.107 / 0.532² = 0.107 / 0.2830 = 0.378
  2. 02g = 0.378 × 9.807 = 3.71 m/s²
  3. 03Mars gravity is about 38% of Earth's.

Ready to run the numbers?

Open Planet Gravity Calculator