Planet Weight Calculator

Weight is a force, the product of an object's invariant mass and the local gravitational acceleration, so moving between worlds changes the reading on a scale without changing the amount of matter present. Surface gravity comes from Newton's law as g = GM divided by r squared, which explains an apparent paradox in the numbers: Saturn is about 95 times more massive than Earth yet has a comparable surface gravity of 10.44 m/s squared, because its equatorial radius of about 60,270 km is over nine times Earth's and the inverse-square term dominates. Working values run from 0.62 m/s squared at Pluto and 1.62 at the Moon, through 3.70 at Mercury, 3.72 at Mars, 8.69 at Uranus, 8.87 at Venus, and 9.81 at Earth, up to 11.15 at Neptune and 24.79 at Jupiter. Two caveats matter when interpreting the table. For the gas giants there is no solid surface, so quoted gravity is referenced to the 1 bar pressure level and is a convention rather than a place anyone could stand. The published figures are also equatorial values that ignore rotation; once the centrifugal term from Jupiter's 9 hour 55 minute day is included, effective equatorial gravity falls to roughly 23.1 m/s squared, and Saturn's drops from 10.44 to about 8.96. Even Earth is not uniform, varying from about 9.78 m/s squared at the equator to 9.83 at the poles. Finally, quoting a result in kilograms is shorthand for weight-equivalent; the underlying mass never changes.

The idea that gravitational acceleration is independent of mass traces to Galileo Galilei's inclined-plane experiments described in his Discorsi of 1638, which undermined the Aristotelian claim that heavier bodies fall faster. Isaac Newton's Principia of 1687 supplied the universal inverse-square law and showed that the same force governs a falling apple and the Moon's orbit. An early empirical hint that g varies came in 1672, when Jean Richer found that his pendulum clock ran slow in Cayenne near the equator compared with Paris, evidence later explained by Earth's rotation and equatorial bulge. Absolute measurement of the gravitational constant came in 1798, when Henry Cavendish used a torsion balance built to John Michell's design to determine Earth's mean density as about 5.48 times that of water, from which G and hence planetary masses could be extracted. Before spacecraft, planetary masses were inferred from the orbits of natural satellites using Kepler's third law, which is why Jupiter's mass was known long before Mercury's was pinned down. The 3rd General Conference on Weights and Measures fixed standard gravity at exactly 9.80665 m/s squared in 1901. Modern values come from radio tracking of orbiters, including MESSENGER at Mercury from 2011, GRAIL's twin spacecraft mapping the lunar field in 2012, Cassini at Saturn from 2004 to 2017, and Juno at Jupiter since 2016.