Free · Gravity calculators 🪐

Gravity from Mass & Center Distance

Relate gravitational acceleration, source mass and distance from its center using Newton’s inverse-square model.

Calculator inputs

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Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

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For a source mass of 10²⁰ kg at a center distance of 1 km, G = 6.67430 × 10⁻¹¹ m³/(kg·s²) gives acceleration 6,674.3 m/s².

g = GM/r²

Enter these known values and leave the other values blank.

This Newtonian model treats the source as a point mass or uses its total mass outside a spherically symmetric body. Distance is measured from its center, not from its surface.
Mass, center distance, G and acceleration are positive. The initial G is 6.67430 × 10⁻¹¹ m³/(kg·s²), a measured constant rather than an exact unit definition.
The calculation excludes rotation, tides, nonspherical structure and relativity. Astronomical and particle-mass selectors use fixed reference values rather than live measurements.

Add altitude to the planet’s radius to get center distance. Use matching length units before adding.

At fixed mass and G, acceleration falls to one quarter because distance is squared in the denominator.

Feet per second squared use exactly 0.3048 meters per second squared, replacing a rounded reciprocal factor.