Force Calculator

How to use this calculator

Fill in two of the three fields. To find the force needed to accelerate a load, enter mass and acceleration. To find how quickly a known force will accelerate an object, enter force and mass. To estimate an unknown mass — for example from a force-sensor reading during a known acceleration — enter force and acceleration.

Acceleration can be given in multiples of standard gravity (g). That is convenient for vehicle and ride engineering, where loads are quoted as "3 g", and for converting a mass into its weight: enter the mass and 1 g, and the force field shows its weight in newtons or pounds-force.

The formula

F = m × a

F: net force
m: mass
a: acceleration

The F in Newton's second law is the net force — the vector sum of every force on the body. If you push a box with 120 N and friction resists with 20 N, the net force that produces acceleration is 100 N. The calculator works with magnitudes along a single direction; a negative force or acceleration simply means "the other way".

Worked example

A 50 kg crate is pushed so that it accelerates at 2 m/s² across a smooth floor. What net force is acting on it?

F = m × a
F = 50 kg × 2 m/s² = 100 N.
In pounds-force: 100 N ÷ 4.448 = 22.5 lbf.

A net horizontal force of 100 N (about 22.5 lbf) is required — more in practice, because friction must also be overcome.

Assumptions and limits

Mass is constant (not a rocket burning fuel).
Force and acceleration point along the same line; for 2-D problems resolve components first.
Classical mechanics: speeds well below the speed of light.

Frequently asked questions

What is the difference between mass and weight?

Mass (kg, lb) measures the amount of matter. Weight is the gravitational force on that mass, W = m g. A 10 kg mass weighs 98.07 N on Earth but only 16.2 N on the Moon.

What is a pound-force?

One lbf is the weight of one pound of mass under standard gravity: exactly 4.4482216152605 N.

Why is my object not accelerating even though I apply a force?

Static friction or other opposing forces can cancel your push. The net force is then zero, and so is the acceleration.

Force Calculator (Newton's Second Law)