Force, mass and acceleration are linked by Newton’s second law. This works out force from the other two — including weight, which is simply the force gravity exerts on a mass.
How it works
Newton’s second law
F = m a
m is mass in kilograms, a is acceleration in metres per second squared, F comes out in newtons.
Weight is a force, computed the same way
An object’s weight is the force gravity exerts on it — mass multiplied by the acceleration due to gravity, 9.80665 m/s² on Earth. Entering an object’s mass with that acceleration gives its weight in newtons, the same figure a physics textbook would give. Mass itself does not change with location, but weight does, because it depends on the local gravitational acceleration — an object weighs roughly a sixth as much on the Moon, where gravity’s pull is weaker, even though its mass is unchanged.
How to use this calculator
- Enter the mass in kilograms.
- Enter the acceleration in metres per second squared — use 9.80665 to find weight under Earth’s gravity.
- Read the resulting force in newtons.
Frequently asked questions
What’s the difference between mass and weight?
Mass is how much matter an object has, unchanged wherever it goes. Weight is the force gravity exerts on that mass, which changes with the local gravitational acceleration — the same object weighs less on the Moon and more on Jupiter, despite having identical mass everywhere.
Why is force measured in newtons?
A newton is defined as the force needed to accelerate one kilogram at one metre per second squared — it follows directly from the mass and acceleration units already in the SI system, rather than being an independently defined unit.
Does this work for forces other than gravity?
Yes — F = ma applies to any net force causing any acceleration, not only gravity. A rocket’s thrust, a car’s braking force, a thrown ball’s launch force are all computed the same way, given the mass being accelerated and the acceleration achieved.
What if there are multiple forces acting on an object?
This calculator computes the net force needed to produce a given acceleration, or the acceleration a given net force produces. If several individual forces act together, they need to be combined (added as vectors) into a single net force first.
Why does a heavier object need more force to reach the same acceleration?
Directly from the equation: force is proportional to mass at a fixed acceleration, so doubling the mass while wanting the same acceleration means doubling the force required — this is the everyday experience of why heavier things are harder to speed up or slow down.
