Weight Calculator
Weight is a force, not a mass. This calculator solves W = m × g in any direction: find weight from mass and gravity, find the mass that produces a known force, or find the gravity behind a measured weight. Switch between metric and imperial units, pick any planet or moon from our solar system, and see the full unit breakdown in one result.
Formula
Worked example
A 70 kg person on Earth: W = 70 × 9.80665 = 686.5 N = 154.3 lbf = 70.0 kgf. The same 70 kg on the Moon (g = 1.62 m/s²): W = 70 × 1.62 = 113.4 N, about one-sixth Earth weight. To reverse-solve: if you know a 70 kg object weighs 686.5 N, divide 686.5 / 70 = 9.807 m/s², confirming Earth gravity.
Weight vs. mass, and three ways to use this calculator
Mass is the amount of matter in an object, measured in kilograms. It is the same on Earth, the Moon, or anywhere in the universe. Weight is the gravitational force on that mass, measured in newtons (or lbf, kgf, etc.), and it changes with location. The relationship is W = m × g, where g is the local surface gravitational acceleration. This calculator solves in any direction. Choose "Solve for weight" to get the force from a known mass and gravity. Choose "Solve for mass" if you know a force and the gravity, for example to find the mass that causes a 500 N spring reading. Choose "Solve for gravity" if you measured a weight and a mass and want to back-calculate the local g, useful for laboratory pendulum experiments or planetary science problems.
Unit choices: newtons, lbf, kgf, poundals, dynes
The SI unit of weight is the newton (N), the force that accelerates 1 kg at 1 m/s². Engineering often uses kilonewtons (kN) for large structures. Kilograms-force (kgf) is what a scale calibrated in kilograms actually reports under Earth gravity: 1 kgf = 9.80665 N. Pound-force (lbf) is the imperial equivalent, where 1 lbf = 4.44822 N. Poundals (pdl) are the coherent imperial unit of force (1 pdl = 0.138255 N). Dynes are the CGS unit (1 N = 100,000 dyn). This calculator shows results in all these units so you can copy the one your textbook, supplier, or data sheet requires.
Gravity across the solar system
Surface gravity depends on a body's mass and radius through Newton's law: g = G × M / r². Jupiter is the heaviest planet but also the largest, so its surface gravity of 24.79 m/s² is about 2.5 times Earth's. Saturn's lower density makes its surface gravity (10.44 m/s²) only slightly higher than Earth's despite being far more massive. Uranus and Neptune both sit near Earth gravity (8.87 m/s² and 11.15 m/s²). The Moon's weak 1.62 m/s² means objects weigh just one-sixth what they do on Earth. Titan and Europa are even lower (1.35 and 1.32 m/s²), and Pluto has the lowest in our list at just 0.62 m/s². The custom gravity option lets you enter any value, useful for other exoplanets or heights above a surface.
Practical applications of W = m × g
Engineers use weight calculations to size structural supports, cranes, lifting equipment, and cable ratings. A beam holding 500 kg produces a downward force of 500 × 9.807 = 4,903 N = 4.90 kN. Scientists use the reverse-solve mode to characterise gravity in the lab: measure the period of a pendulum or the deflection of a spring scale and back-calculate g. Aerospace engineers convert mass to weight in different planetary environments to design landing gear and habitats. Nutritionists and clinicians use kilograms-force because bathroom scales report in kg under Earth gravity, effectively reading kgf and labelling it kg. Knowing the exact conversion (1 kgf = 9.80665 N, not 9.81 N) matters when high precision is required.
Surface gravity across the solar system
| Body | g (m/s²) | Weight of 70 kg (N) | Weight of 70 kg (lbf) | vs. Earth |
|---|---|---|---|---|
| Sun | 274 | 19,180 | 4,311 | 27.97x |
| Jupiter | 24.79 | 1,735 | 390 | 2.53x |
| Neptune | 11.15 | 781 | 175 | 1.14x |
| Saturn | 10.44 | 731 | 164 | 1.07x |
| Earth | 9.807 | 686 | 154 | 1.00x |
| Uranus | 8.87 | 621 | 140 | 0.90x |
| Venus | 8.87 | 621 | 140 | 0.90x |
| Mars | 3.71 | 260 | 58 | 0.38x |
| Mercury | 3.70 | 259 | 58 | 0.38x |
| Moon | 1.62 | 113 | 25 | 0.17x |
| Titan | 1.35 | 95 | 21 | 0.14x |
| Europa | 1.315 | 92 | 21 | 0.13x |
| Pluto | 0.62 | 43 | 10 | 0.06x |
Gravitational acceleration and the weight of a 70 kg mass on 13 bodies. Earth uses the exact standard g = 9.80665 m/s².
Frequently asked questions
What is the difference between weight and mass?
Mass is the amount of matter in an object, measured in kilograms, and never changes with location. Weight is the gravitational force on that mass, measured in newtons, and changes with the local gravity g. The two are linked by W = m × g. A 70 kg person always has a mass of 70 kg, but weighs 686 N on Earth and only 113 N on the Moon.
How do I calculate weight from mass in pounds?
Select "Pounds (lb)" in the mass unit dropdown, enter your mass in pounds, and the calculator converts to kilograms internally before multiplying by g. The result in pound-force (lbf) matches what your bathroom scale would read in pounds under Earth gravity (because lbf and the pound-mass are numerically equal under standard gravity).
What is a kilogram-force (kgf) and how does it differ from a newton?
One kilogram-force is the force exerted by standard gravity on a one-kilogram mass: 1 kgf = 9.80665 N exactly. A bathroom scale calibrated in kilograms is really reading kilograms-force. The newton is the SI unit and is dimensionally consistent, while kgf mixes force and mass units. For high-precision work always use newtons.
How do I find the gravity of an unknown planet?
Select "Solve for gravity" mode. Enter the weight you measured (in any force unit) and the mass of the object (in kg). The calculator divides weight by mass to give g in m/s², then shows how it compares to Earth standard gravity.
Why does Jupiter have higher gravity than Earth even though it is less dense?
Surface gravity depends on both mass and radius: g = G × M / r². Jupiter is about 318 times more massive than Earth, which overwhelms its larger radius. The result is about 2.5 times Earth gravity at its cloud tops. Saturn, despite being almost as large as Jupiter, has a very low average density (less than water), so its surface gravity is only slightly above Earth's.
How do I convert weight from newtons to pound-force?
Divide newtons by 4.44822162. For example, 686.5 N ÷ 4.44822 = 154.3 lbf. Equivalently, multiply by 0.22481. The calculator shows this conversion automatically in the results panel.