Surface gravity is how strongly a planet or moon pulls on objects at its surface, which is why you'd weigh differently on Mars or the Moon than on Earth.
Surface gravity is how strongly a planet or moon pulls on objects at its surface, which is why you'd weigh differently on Mars or the Moon than on Earth. This calculator finds surface gravity from a body's mass and radius.
Mars has a mass of 6.39×10²³ kg and a radius of 3.3895×10⁶ m. g = (6.674×10⁻¹¹ × 6.39×10²³) / (3.3895×10⁶)² ≈ 3.71 m/s² — matching Mars's known surface gravity, about 38% of Earth's.
g = GM ÷ r², using mass and radius of the body.
A larger radius spreads the same mass over more area, reducing surface gravity.
Mars has significantly less mass and a smaller radius, combining to about 38% of Earth's gravity.