Weight Calculator (W = mg)

This weight calculator finds weight from mass using W equals mg, where g is the strength of gravity. Choose the unknown and enter the others; the calculator solves for weight, mass or the gravitational field strength. Weight is a force, measured in newtons, and is the pull of gravity on a mass, so it changes with location: the same mass weighs less on the Moon than on Earth. The default g is Earth\u2019s 9.81 metres per second squared, but you can change it for the Moon, Mars or anywhere else. The formula, a worked example and the assumptions are below.

Weight (N)

Mass (kg)

Gravity (m/s\u00B2)

Solve for

Value

Result

The formula

Weight is W = mg, where m is mass in kilograms and g is the gravitational field strength in metres per second squared (or newtons per kilogram). Rearranged: m = W / g and g = W / m.

Worked example

A 10 kg mass on Earth (g = 9.81) weighs W = 10 times 9.81 = 98.1 N. On the Moon, with g about 1.62, the same mass weighs about 16.2 N. Solve for W with m = 10, g = 9.81 to confirm.

Frequently asked questions

What is the difference between mass and weight?

Mass is the amount of matter, in kilograms, and never changes. Weight is the gravitational force on that mass, in newtons, and depends on g.

What value of g should I use?

9.81 metres per second squared on Earth. Use about 1.62 for the Moon or 3.71 for Mars.

Why is weight measured in newtons?

Because weight is a force, and the SI unit of force is the newton.

Who this calculator is for

This calculator is for physics students, teachers and engineers.

What this calculator assumes

You enter SI units as labelled.
One variable is solved from the others.
Results are rounded for display.

Formula and sources

Related calculators

Kinetic Energy Calculator: energy of motion.
Momentum Calculator: mass times velocity.
Projectile Motion Calculator: range and height.

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