Force Calculator
Calculate force from mass and acceleration — Newton's second law — in newtons, kilonewtons, kilograms-force and pounds-force.
Mass times acceleration, in newtons and the older units.
How the force calculator works
Newton's second law: force = mass × acceleration. With acceleration set to g (9.80665 m/s²) the result is the object's weight — what the scales push back with. One newton is the force that gives 1 kg an acceleration of 1 m/s²; a kilogram-force (kgf) is the weight of 1 kg, 9.80665 N; a pound-force is 4.448 N.
Enter any acceleration to find the force behind a launch, a stop or a lift.
Formula: F = m a
Worked examples
| Inputs | Force | Note |
|---|---|---|
| 10 kg at g (its weight) | 98.07 N | 98.07 N = 10 kgf |
| 1,500 kg car at 3 m/s² | 4,500 N | 4.5 kN |
| 0.145 kg ball at 2,000 m/s² | 290 N | a bat strike: 290 N |
FAQFrequently asked questions
Is weight a force?
Yes — mass × g. Mass is the same on the Moon; weight is a sixth of it because g is 1.62 m/s² there.
What is a newton in everyday terms?
About the weight of a small apple (100 g). A liter of water weighs 9.8 N.
What is a kilogram-force?
The weight of one kilogram under standard gravity, 9.80665 N. Old spring balances and torque figures in kgf·m still use it.
How does F = ma relate to momentum?
Acceleration is the rate of change of velocity, so ma is the rate of change of momentum — Newton's original wording.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Institute of Standards and Technology — the US measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.