By Zencalcy Editorial TeamLast reviewed About us
Every pair of masses attracts every other pair with a force proportional to both masses and inversely proportional to the square of the distance between their centres. The constant of proportionality, G, is tiny, so the attraction is only noticeable when at least one mass is planetary.
Newton's law of gravitation between two masses.
F = G m₁ m₂ / r²
G = 6.6743 × 10⁻¹¹ m³ kg⁻¹ s⁻². r is measured between centres of mass, so for an object on Earth's surface use the Earth's radius plus the object's height.
| Symbol | Meaning |
|---|---|
| F | Gravitational force of attraction, in newtons. |
| G | Gravitational constant, 6.6743 × 10⁻¹¹ m³ kg⁻¹ s⁻². |
| m₁, m₂ | The two masses, in kilograms. |
| r | Distance between the centres of mass, in metres. |
Earth's mass is 5.972 × 10²⁴ kg and its radius 6.371 × 10⁶ m. The force on a 70 kg person is about 687 N — the familiar weight, recovered from G and planetary data alone.
Continue with the Impact Force Calculator, Net Force Calculator, or the Normal Force Calculator — or browse more dynamics tools and all physics calculators.
Gravity is by far the weakest fundamental interaction. G is small because the force between everyday masses is tiny; it takes a planet-sized mass to make it noticeable.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026