Force Calculator
Apply Newton's second law to find force, mass or acceleration.
About the Force Calculator
Newton's second law links three quantities: the net force on an object, its mass, and the acceleration that results. Push twice as hard and the acceleration doubles; push the same on twice the mass and it halves. Choose what to solve for and enter the other two.
One newton (N) is the force that accelerates 1 kg at 1 m/s². Weight is a force too: on Earth a 1 kg mass weighs about 9.81 N, because gravity accelerates it at 9.80665 m/s². The result also shows pound-force (1 lbf = 4.4482216152605 N exactly) and kilogram-force.
The formula
F = m × a
- F
- net force, in newtons (N)
- m
- mass, in kilograms (kg)
- a
- acceleration, in metres per second squared (m/s²)
How to read your result
- The force is the net (overall) force. If friction or drag also act, the engine or push must supply more than this.
- A negative answer means the force points opposite to the direction you treated as positive, for example braking.
Worked example
A 1,200 kg car speeding up at 2.5 m/s²
- F = m × a = 1,200 × 2.5
- F = 3,000 N
- In pound-force: 3,000 ÷ 4.448 = 674.4 lbf
Things to keep in mind
- Uses SI units: convert grams to kilograms (÷ 1,000) and km/h changes to m/s (÷ 3.6) first.
- Classical mechanics: accurate for everyday speeds, not close to the speed of light.
Questions people ask
What's the weight of 1 kg?
About 9.81 N on Earth (1 kg × 9.80665 m/s²). On the Moon the same kilogram weighs about 1.62 N.
How do I find acceleration from force?
Choose Acceleration under Solve for: a = F ÷ m. A 500 N push on an 80 kg sled with no friction gives 6.25 m/s².
What is a kilogram-force?
The weight of 1 kg in standard gravity: 1 kgf = 9.80665 N. It is an older unit still seen on scales and engineering drawings.