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Force Calculator
Solve Newton's second law, F = m × a, for force, mass or acceleration with the units you have. The calculator also shows what the mass weighs on every planet, the Moon and Pluto.
Solve for
Enter your values to see the result.
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How to use the Force Calculator
- Choose what to solve for: force, mass or acceleration.
- Enter the two known values and pick their units.
- Press Calculate; results also update as you type.
- Read the answer in SI and other units.
- See the planet table to compare the weight of the mass across the solar system.
Newton's second law
F = m × a, so m = F / a and a = F / m. Use kilograms, metres per second squared and newtons together (1 N = 1 kg·m/s²). Weight is the special case where the acceleration is the local gravity: W = m × g.
Example: a 1,500 kg car accelerating at 3 m/s² needs a net force of 1,500 × 3 = 4,500 N (about 1,012 lbf).
Surface gravity in the solar system
| Body | Gravity (m/s²) | Relative to Earth | Weight of 70 kg (N) |
|---|---|---|---|
| Mercury | 3.70 | 0.38 | 259 |
| Venus | 8.87 | 0.90 | 621 |
| Earth | 9.81 | 1.00 | 686 |
| Moon | 1.62 | 0.17 | 113 |
| Mars | 3.71 | 0.38 | 260 |
| Jupiter | 24.79 | 2.53 | 1,735 |
| Saturn | 10.44 | 1.06 | 731 |
| Uranus | 8.69 | 0.89 | 608 |
| Neptune | 11.15 | 1.14 | 780 |
| Pluto | 0.62 | 0.06 | 43 |
Gravity values are approximate equatorial surface (or cloud-top, for the gas giants) values from NASA planetary fact sheets.
Force unit conversions
1 N = 0.224809 lbf = 0.101972 kgf = 100,000 dyn · 1 lbf = 4.44822 N · 1 kgf = 9.80665 N.
Frequently asked questions
What is the formula for force?
Newton's second law: F = m × a. Net force in newtons equals mass in kilograms times acceleration in metres per second squared. It rearranges to m = F / a and a = F / m.
What is a newton?
One newton (N) is the force that gives a 1 kg mass an acceleration of 1 m/s². 1 N ≈ 0.2248 pound-force, and the weight of a 102 g apple on Earth is about 1 N.
What is the difference between mass and weight?
Mass, in kilograms, is the amount of matter and is the same everywhere. Weight is the gravitational force on that mass, W = m × g, measured in newtons, so it changes from planet to planet.
How much would I weigh on Mars?
Mars' surface gravity is about 3.71 m/s², roughly 38% of Earth's. A 70 kg person weighs about 260 N on Mars, which a bathroom scale calibrated for Earth would show as about 26.5 kg.
How do I convert newtons to pounds-force?
Divide by 4.44822: 1 lbf = 4.44822 N. For example 500 N ≈ 112.4 lbf.
What is kilogram-force?
One kilogram-force (kgf) is the weight of 1 kg under standard gravity, exactly 9.80665 N. It is not an SI unit but appears on older scales and specifications.
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