Softonic

Force Calculator

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Force is what changes an object’s motion, and Newton’s second law ties it to two things you can measure: how much matter is moving (mass) and how quickly its velocity is changing (acceleration). Enter a mass in kilograms and an acceleration in metres per second squared, and this calculator returns the resulting force in newtons (N) and pounds-force (lbf). Leave acceleration at 9.81 m/s² to read the weight of an object in Earth’s gravity, or set your own value for thrust, braking, or any other scenario.

How to use the calculator

  1. 1

    Enter the mass

    Type the object's mass in kilograms (kg).

  2. 2

    Enter the acceleration

    Use 9.81 m/s² for gravity on Earth, or any acceleration you are applying.

  3. 3

    Read the force

    The result appears instantly in newtons and pounds-force.

The formula

Newton’s second law states that the net force on an object equals its mass times its acceleration:

F = m × a

Where:

  • F = force, measured in newtons (N). One newton is the force needed to accelerate 1 kg by 1 m/s².
  • m = mass, measured in kilograms (kg).
  • a = acceleration, measured in metres per second squared (m/s²).

To convert the result to pounds-force, multiply newtons by 0.224809.

Worked example

A 70 kg person standing still on Earth experiences gravitational acceleration of 9.81 m/s². The downward force, their weight, is:

F = 70 kg × 9.81 m/s² = 686.7 N

In pounds-force that is 686.7 × 0.224809 ≈ 154.4 lbf. Note that the 70 kg is their mass everywhere in the universe, but the 686.7 N is their weight only on Earth.

Quick reference

Mass (kg) Acceleration (m/s²) Force (N) Force (lbf)
1 9.81 9.81 2.20
10 9.81 98.1 22.05
70 9.81 686.7 154.37
1000 1 1000 224.81
5 2 10 2.25

Common pitfalls

  • Mass vs. weight. Mass (kg) is the amount of matter; weight (N) is the force gravity exerts on it. The Moon’s gravity is about 1.62 m/s², so the same mass weighs roughly one-sixth as much there.
  • Unit mixing. F = m × a only gives newtons when mass is in kg and acceleration in m/s². Pounds, grams, or feet need conversion first.
  • Net force only. The F in the formula is the net (resultant) force. If several forces act at once, add them as vectors before plugging in.
  • Direction matters. Force is a vector. A negative acceleration (deceleration) produces a force in the opposite direction of motion.

Frequently Asked Questions

It states that the net force on an object equals its mass multiplied by its acceleration, written F = m × a. A larger mass or a greater acceleration both produce a larger force.

A newton (N) is the SI unit of force. One newton is the force required to accelerate a 1 kg mass at 1 m/s². As a rough feel, holding a small apple (about 100 g) against gravity takes roughly 1 N.

Multiply the force in newtons by 0.224809 to get pounds-force (lbf). For example, 100 N × 0.224809 ≈ 22.48 lbf. This calculator shows both units automatically.

The values you enter are sent to our servers only to compute the result. They are not stored or shared. When you use the step-by-step wizard, the values also travel in the page link between steps, so avoid sharing links that contain numbers you want to keep private.

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