Solve force, mass or acceleration. This free force calculator uses Newton’s second law F = m x a, with a gravity preset for weight, and shows force in newtons, pounds-force and kilograms-force.
Enter the two known values and the calculator finds the third using Newton’s second law, F = m x a. Force is in newtons (N), mass in kilograms, acceleration in m/s2.
Newton’s second law: F = m x a. One newton accelerates 1 kg at 1 m/s2. Weight is force from gravity: W = m x g, with g approximately 9.81 m/s2 on Earth.
How the Force Calculator Works
This tool solves Newton’s second law for whichever value you don’t know — force, mass, or acceleration — and can also use standard gravity to turn a mass into its weight.
Formula: F = m × a (Newton’s second law). Rearranged: m = F ÷ a, or a = F ÷ m. To find weight specifically, set a = g = 9.80665 m/s² (Earth’s standard gravity), so W = m × g.
- Solve for — toggle that picks whether the calculator solves for Force, Mass, or Acceleration
- Force (F) — the net force, entered or returned in newtons (N)
- Mass (m) — the object’s mass in kilograms (kg)
- Acceleration (a) — the rate of change of velocity in m/s², with a one-tap button to fill in gravity (9.80665 m/s²)
Example Scenarios
| Mass (kg) | Acceleration (m/s²) | Force (N) |
|---|---|---|
| 10 | 9.8 (gravity) | 98 N |
| 5 | 4 | 20 N |
| 1,200 (car) | 3 | 3,600 N |
| 70 (person) | 9.8 (gravity) | 686 N |
| 2 | 15 | 30 N |
| 500 | 2.5 | 1,250 N |
Force Calculator FAQ
What units does this force calculator use?
Force is calculated in newtons (N), the SI unit, since one newton accelerates one kilogram at one metre per second squared. The results panel also converts that figure to pounds-force (lbf) and kilograms-force (kgf) automatically.How do I calculate the weight of an object with this tool?
Enter the object’s mass in kilograms, then tap “Use gravity g = 9.80665 m/s²” to fill the acceleration field with standard Earth gravity. The Force result is then the object’s weight, shown in newtons, lbf, and kgf.Can I solve for mass or acceleration instead of force?
Yes. Use the “Solve for” toggle to switch the calculator’s target between Force, Mass, and Acceleration. Enter the two values you know and it computes the third using F = m × a.What’s the difference between kgf and newtons?
Kilogram-force (kgf) is the force exerted by gravity on one kilogram of mass under standard gravity, roughly 9.80665 N. Newtons are the SI unit of force and don’t assume any particular gravity value.Why did my acceleration or mass field disappear?
The calculator only shows the two input fields it needs based on which value you’re solving for. Switch the “Solve for” toggle to reveal the field you want to enter instead.Does this calculator account for friction or other opposing forces?
No. It applies Newton’s second law directly (net force = mass × acceleration), so the result represents the net force needed to produce that acceleration, not any individual real-world force like friction or air resistance.Related Calculators
Once you’ve found a force, you may want to see how much energy that motion carries with the kinetic energy calculator, check the mass-per-volume of the material involved using the density calculator, or explore other physics relationships with the half-life decay calculator.