How to use the weight calculator
- Enter the mass and choose kilograms, pounds, grams or metric tons.
- Choose where you want the weight: Earth, the Moon, a planet or Pluto, or Other to type your own gravitational acceleration.
- Read the weight in newtons, pound-force and kilogram-force, and the table showing the same mass across the solar system.
The weight formula
Weight is a force: the pull of gravity on a mass. Newton's second law gives it directly:
One newton is the force that accelerates 1 kg at 1 m/s². Standard gravity, 9.80665 m/s², is the exact reference value used by NIST and the international system of units; it also defines the pound-force and the kilogram-force, which is why 1 kg weighs exactly 1 kgf on Earth. Gravity for the other bodies comes from the NASA Planetary Fact Sheet, which gives the value at the equator including the effect of rotation, and for the gas giants at the level where the atmospheric pressure is 1 bar.
Worked example
The default is a 70 kg person on Earth:
- W = 70 kg × 9.80665 m/s² = 686.47 N
- In pound-force: 686.47 ÷ 4.44822 = 154.32 lbf
- In kilogram-force: 686.47 ÷ 9.80665 = 70 kgf
- On the Moon: 70 × 1.6 = 112 N, or 25.2 lbf, about a sixth of the Earth figure
Enter 150 lb instead and the mass is 150 × 0.45359237 = 68.039 kg, so the weight on Earth is 68.039 × 9.80665 = 667.23 N, or exactly 150 lbf.
Weight of 70 kg across the solar system
| Body | g (m/s²) | Weight (N) | Weight (lbf) | A scale would show |
|---|---|---|---|---|
| Mercury | 3.7 | 259 | 58.2 | 26.4 kg |
| Venus | 8.9 | 623 | 140.1 | 63.5 kg |
| Earth | 9.81 | 686 | 154.3 | 70.0 kg |
| Moon | 1.6 | 112 | 25.2 | 11.4 kg |
| Mars | 3.7 | 259 | 58.2 | 26.4 kg |
| Jupiter | 23.1 | 1,617 | 363.5 | 164.9 kg |
| Saturn | 9.0 | 630 | 141.6 | 64.2 kg |
| Uranus | 8.7 | 609 | 136.9 | 62.1 kg |
| Neptune | 11.0 | 770 | 173.1 | 78.5 kg |
| Pluto | 0.7 | 49 | 11.0 | 5.0 kg |
"A scale would show" is the reading of a bathroom scale calibrated on Earth, which really measures force and divides by 9.80665. Saturn, Uranus and Neptune pull about as hard as Earth despite their huge mass, because their 1-bar level is far from the center.
Weight varies on Earth too
Standard gravity is a convention. Real gravity is about 9.780 m/s² at the equator and 9.832 m/s² at the poles, because Earth spins and bulges at the equator, and it falls slightly with altitude. The same 70 kg person weighs about 3.6 N (0.8 lbf) more at the North Pole than in Ecuador. That is why precise laboratory balances compare masses rather than measuring force, and why a spring scale reads differently in different places. To go the other way and find a mass from a measured weight, use the mass calculator.
Frequently asked questions
What is the difference between weight and mass?
Mass is how much matter an object has, in kilograms or pounds, and it never changes. Weight is the force of gravity on it, in newtons or pound-force, and it depends on where you are. On the Moon your mass is the same but your weight is about one-sixth.
How many newtons is 1 kg?
On Earth, 1 kg weighs 9.80665 N under standard gravity, so about 9.8 N. For quick estimates, many people round to 10 N per kilogram.
How much would I weigh on Mars?
About 38% of your Earth weight, since Mars's gravity is 3.7 m/s². A person who weighs 154 lbf on Earth would weigh about 58 lbf there, even though their mass is still 70 kg.
Why does my scale show kilograms if weight is a force?
Bathroom scales measure the force you press down with and divide it by Earth's standard gravity to display a mass. That works well on Earth but would give the wrong mass on the Moon or Mars.
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