Force Calculator (F = ma)
Force calculator using Newton’s second law F = m·a: find net force, mass or acceleration in N, lbf, kgf and more.
F = m · a
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
Newton’s second law states that the net force on a body equals its mass times its acceleration, F = m·a. One newton accelerates 1 kg at 1 m/s².
F is the net (resultant) force: add all forces as vectors first. Weight is the special case F = m·g.
Formula
F = m · a
| Symbol | Quantity | Units |
|---|---|---|
| m | Mass | kg, g, mg, µg, t, lb, oz, st, US ton, ct, Da |
| a | Acceleration | m/s², ft/s², g, Gal |
| F | Net force | N, kN, mN, dyn, lbf, kgf |
Worked example
Given: m = 10 kg · a = 2 m/s²
F = m · a
Result: F = 20 N
Net force for different values of Mass
| m · Mass | F · Net force |
|---|---|
| 5 kg | 10 N |
| 7.5 kg | 15 N |
| 9 kg | 18 N |
| 10 kg | 20 N |
| 11 kg | 22 N |
| 12.5 kg | 25 N |
| 15 kg | 30 N |
| 20 kg | 40 N |
Other values as in the worked example.
Frequently asked questions
What is the weight of a 70 kg person?
W = m·g = 70 × 9.81 = 687 N, about 154 lbf.
Is F = ma valid at high speeds?
Only well below the speed of light. Near it, relativistic mechanics is needed.
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