Weight is a force: the pull of a planet’s gravity on a mass. This calculator turns a mass into a weight on Earth, the Moon, any planet, Pluto or the Sun’s visible surface, and runs the same formula backward to recover the mass or the local gravity from a measured weight. Alongside the answer it lists the weight on every world in its table and what an ordinary bathroom scale would display there.
How to use the weight calculator
- Under Solve for, choose Weight, Mass or Gravity (g).
- Select a body in On which world?. Pick Custom value to enter your own gravitational acceleration, for example a measured local g. This menu is hidden when you solve for g.
- Enter the known values: the Mass (m) in kg, g, lb, oz, stone or tons, and/or the Weight (W) in N, kN, lbf, kgf, dyn or ozf.
- Read the answer in the unit chosen under Show the result in. The result adds other units, the bathroom-scale reading and a table of the same mass’s weight on all eleven worlds.
Mass, weight and g must all be greater than zero.
Weight formula
With m in kilograms and g in m/s², the weight comes out in newtons. Weight is the special case of F = ma in which the acceleration is the free-fall acceleration, and it points toward the center of the planet.
Worked example: 70 kg on Earth and the Moon
On Earth at standard gravity: W = 70 kg × 9.80665 m/s² = 686.47 N, which is about 154.3 lbf or exactly 70 kgf.
On the Moon: W = 70 kg × 1.62 m/s² = 113.4 N (25.49 lbf). An Earth-calibrated scale would show 113.4 ÷ 9.80665 = 11.56 kg.
The kilogram-force is defined with standard gravity, which is why 70 kg weighs exactly 70 kgf on Earth’s preset and nowhere else.
Weight across the Solar System
These are the surface gravities the calculator uses, rounded from NASA planetary fact sheets. They are approximate equatorial values; for the gas giants, the “surface” is the cloud level where pressure is 1 bar.
| World | g (m/s²) | Weight of 70 kg | Earth scale reads |
|---|---|---|---|
| Earth (standard) | 9.80665 | 686.5 N | 70.0 kg |
| Moon | 1.62 | 113.4 N | 11.6 kg |
| Mercury | 3.70 | 259.0 N | 26.4 kg |
| Venus | 8.87 | 620.9 N | 63.3 kg |
| Mars | 3.71 | 259.7 N | 26.5 kg |
| Jupiter | 24.79 | 1,735.3 N | 177.0 kg |
| Saturn | 10.44 | 730.8 N | 74.5 kg |
| Neptune | 11.15 | 780.5 N | 79.6 kg |
| Pluto | 0.62 | 43.4 N | 4.4 kg |
Uranus has nearly the same g as Venus, and the Sun’s photosphere (274 m/s²) would make the same person weigh 19,180 N. Saturn is far more massive than Earth, but its huge radius keeps its cloud-top gravity only slightly higher.
Standard gravity versus local gravity
Standard gravity, g₀ = 9.80665 m/s², was adopted by the General Conference on Weights and Measures in 1901 and is exact by definition. The real value where you stand is different. Earth’s rotation and its slightly flattened shape give about 9.78 m/s² at the equator and 9.83 m/s² at the poles, and gravity weakens a little with altitude.
The effect is small but measurable: with Custom value, 70 kg weighs 684.6 N at 9.78 m/s² and 688.2 N at 9.832 m/s², a difference of about half a percent. A beam balance compares two masses directly, so it reads the same anywhere; that is also why precision electronic balances are calibrated with reference masses where they are installed.
Solving for mass or gravity
Solving for mass answers “how much stuff produces this force?” — 150 lbf on Earth is 68.04 kg, which is exactly 150 lb, because the pound-force is defined with standard gravity. Solving for g answers “how strong is gravity here?” If an 80 kg test mass weighs 300 N, then g = 3.75 m/s², or 0.382 times Earth’s standard gravity, close to the value on Mars.
For the full Newton’s-law version with any acceleration, use the force calculator; to see how long a drop takes under each gravity, try the free fall calculator.
Frequently asked questions
What is the difference between mass and weight?
Mass is the amount of matter in an object, measured in kilograms or pounds, and it is the same everywhere. Weight is the gravitational force on that mass, measured in newtons or pound-force, and it changes with the local gravity. A 70 kg person weighs 686.5 N on Earth but 113.4 N on the Moon.
How much would I weigh on the Moon?
About one-sixth as much. With the Moon's surface gravity of roughly 1.62 m/s², a 70 kg person weighs 113.4 N, and a bathroom scale calibrated on Earth would read about 11.6 kg (25.5 lb). Their mass is still 70 kg.
Why does a bathroom scale show kilograms if weight is a force?
The scale measures the force pressing down on it, then divides by an assumed g to display a mass. That conversion is calibrated for Earth, so on another world the same scale shows the wrong mass but correctly reflects how heavy you feel.
Is g exactly 9.81 m/s² everywhere on Earth?
No. Local gravity ranges from about 9.78 m/s² at the equator to 9.83 m/s² at the poles, and it falls slightly with altitude. Standard gravity, 9.80665 m/s², is a fixed conventional value used for unit definitions and calculations.
How do I find mass from weight?
Divide the weight by g: m = W ÷ g. A weight of 600 N on Earth corresponds to 600 ÷ 9.80665 = 61.18 kg, or about 134.9 lb.