Force Calculator
Force, mass and acceleration (F = m × a).
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Newton's second law says force equals mass times acceleration. Enter any two of the three and this calculator finds the third — or switch acceleration to gravity to work out an object's weight in newtons.
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Force — The Quick Answer
Force equals mass times acceleration (F = m × a), measured in newtons. One newton accelerates a one-kilogram mass at one metre per second squared. For weight, use a = g ≈ 9.81 m/s².
Shortcut
F = m × a | m = F ÷ a | a = F ÷ m | Weight = m × g
The three relationships
| Quantity | Symbol | Unit | Formula |
|---|---|---|---|
| Force | F | newtons (N) | F = m × a |
| Mass | m | kilograms (kg) | m = F ÷ a |
| Acceleration | a | m/s² | a = F ÷ m |
| Weight | W | newtons (N) | W = m × g |
Weight and mass aren't the same thing: mass is how much matter an object has (in kg), while weight is the gravitational force on it (in newtons). A 70 kg person weighs about 687 N on Earth and only about 114 N on the Moon, but their mass stays 70 kg.
How It Works
The Formula
Newton's second law
Formula
F = m × a m = F / a a = F / m W = m × g
Variables
Force (newtons)
The push or pull applied to an object. One newton (N) = 1 kg·m/s².
Mass (kilograms)
The amount of matter in the object. It doesn't change with location.
Acceleration (m/s²)
How quickly velocity changes. On Earth's surface, gravity gives a = g ≈ 9.81 m/s².
Note: This is the net force — the sum of all forces acting on the object. If you're applying several forces, add them as vectors (with direction) before solving.
Last updated: October 6, 2026
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Frequently Asked Questions
What is the formula for force?
F = m × a (Newton's second law): force equals mass times acceleration. A 10 kg mass accelerating at 2 m/s² experiences a force of 10 × 2 = 20 newtons.
How do I calculate weight in newtons?
Multiply mass by gravitational acceleration: W = m × g, with g ≈ 9.80665 m/s² on Earth. A 70 kg person therefore weighs about 70 × 9.80665 ≈ 686.5 N.
What's the difference between mass and weight?
Mass (kg) measures how much matter is in an object and is constant everywhere. Weight (N) is the gravitational force on that mass and changes with gravity — so the same object weighs less on the Moon, where g is about 1.62 m/s².
What is one newton?
One newton is the force needed to accelerate a 1 kg mass at 1 m/s². It's a modest force — roughly the weight of a small apple (about 100 g) resting in your hand.