How to Calculate Weight on Other Planets

Your mass is the same no matter what planet you’re on, but your weight changes because gravity is different. The reason gravity is different is because other planets have different masses and diameters from Earth. If you know your weight on Earth, it’s easy to calculate your weight on another planet using that planet’s surface gravity.

Estimate Your Weight From a Chart

If you just want an estimate of your weight on another planet in the solar system, simply look up the number closest to your weight on Earth. It doesn’t matter whether you use pounds or kilograms because the conversion factor is the same.

Gravity depends on how far the surface of a planet is from its center, which leads to some surprising results. Even though Saturn is much more massive than Earth, it’s also much larger. So, if you stand on the surface of Saturn, you only weight slightly more than on Earth. You would weigh about the same on Mars and Mercury, even though Mars is more massive. This is because Mars has a larger diameter. The same effect is seen when comparing gravity on Venus and Uranus. Uranus, like Saturn, is a gas giant. Even though it’s massive, it’s huge. Your weight on Venus and Uranus (using the edge of its clouds as its “surface”) would be about the same.

How to Calculate Weight on Other Planets

Calculate your weight on another planet by multiplying your weight times the relative surface gravity of the other world.

Weight on Other Planet = Weight on Earth x Multiple of Earth’s Gravity

For example, let’s calculate your weight on Neptune if you weigh 158 lbs on Earth. Gravity on Neptune is 1.19 time higher than on Earth.

Weight on Neptune = 158 lbs x 1.19
Weight on Neptune = 188 lbs

You can use the same process if you measure weight in kilograms. If you weigh 81 kg, let’s find your weight on Pluto.

Weight on Pluto = 81 kg x 0.06
Weight on Pluto = 4.9 kg

How Do We Know the Gravity of Other Planets?

Scientists can estimate gravity on other planets, even ones we haven’t visited, using Newton’s law of gravitation:

F = G*m₁*m₂/r²

Here, F is the gravitation force between two objects, G is the gravitational constant, m₁ and m₂ are the masses of two bodies, and r is the radius of the distance between the centers of the two bodies.

First, we can measure the size of a planet. If the planet has a moon, then gravity is known from its orbit (r). Actually, solving for the gravitational force is the first step to estimating the mass of a planet. If the planet doesn’t have a moon, we estimate its surface gravity from slight perturbations in its orbit from the effects of nearby planets. To find the gravity of an asteroid, it’s necessary to send a probe past the body to measure the deflection of radio signals.

Gravity isn’t really a single value for a planet. A planet isn’t a perfect sphere, with a round core, mantle, and crust! For example, on Earth, gravity varies about 0.7%. The lowest value is 9.7639 m/s² on the Nevado Huascarán mountain in Peru, while the highest value is 9.8337 m/s² on the Arctic Ocean surface. Gravity varies with latitude, altitude, topology, geography, and other factors. So, when you calculate your weight on another planet, keep in mind it’s only an estimate. If you visit that world, your weight might be slightly lower or higher.

References

• Halliday, David; Robert Resnick; Kenneth S. Krane (2001). Physics v. 1. New York: John Wiley & Sons. ISBN 978-0-471-32057-9.
• Hodgeman, Charles, ed. (1961). Handbook of Chemistry and Physics (44th ed.). Cleveland, USA: Chemical Rubber Publishing Co. pp. 3480–3485.
• Serway, Raymond A.; Jewett, John W. (2004). Physics for Scientists and Engineers (6th ed.). Brooks/Cole. ISBN 978-0-534-40842-8.
• Thorne, Kip S.; Misner, Charles W.; Wheeler, John Archibald (1973). Gravitation. W.H. Freeman. ISBN 978-0-7167-0344-0.