Gravity Calculator

How it works

1. 1Select a preset body (Earth, Moon, Mars, Jupiter, Sun) or choose “Custom” and enter a mass M in kg and radius r in metres.
2. 2The calculator applies Newton’s law of gravitation: g = G·M ÷ r², where G ≈ 6.674×10⁻¹¹ N·m²/kg².
3. 3Results show surface gravity in m/s², its ratio to Earth gravity (9.80665 m/s²), and the weight a 1 kg mass would have there.

Use cases

• Students verifying textbook surface-gravity values for solar-system bodies.
• Writers and game designers calculating realistic gravity for fictional planets.
• Engineers estimating gravitational effects for space-mission and payload planning.

Frequently asked questions

What formula does this calculator use?

It uses g = G·M ÷ r², where G ≈ 6.674×10⁻¹¹ N·m²/kg² is the gravitational constant, M is the body’s mass in kg, and r is its mean radius in metres, giving the surface field strength in m/s².

Can you show a worked example for Earth?

Earth has M ≈ 5.972×10²⁴ kg and r ≈ 6.371×10⁶ m. So g = (6.674×10⁻¹¹ × 5.972×10²⁴) ÷ (6.371×10⁶)² ≈ 9.82 m/s², matching the accepted ~9.8 m/s² (mean vs equatorial radius accounts for the tiny difference).

Why is Jupiter’s gravity only about 2.5× Earth’s if it is far more massive?

Surface gravity depends on mass and radius. Jupiter is ~318× more massive but ~11× larger in radius, and gravity falls off as r², so the large radius offsets most of the mass. The result is g ≈ 24.8 m/s², about 2.5× Earth’s.