Friction Force Calculator (Coefficient of Friction)
By Santaji GadepatilinUpdated October 29, 2026
Friction opposes sliding between two surfaces and is proportional to how hard they are pressed together. This friction force calculator uses F = μN to find the friction force, the normal force or the coefficient of friction, for an object resting on a level surface or any known normal force.
How to use the friction force calculator
Enter the coefficient of friction and the mass of an object on a level surface — the normal force N = mg is calculated for you — and you get the friction force. For a sloped surface or an extra pressing force, clear the mass and enter the normal force directly, or use the inclined plane calculator.
Friction formula
Ff = μ × N · N = m × g (level surface)
Example
A 10 kg crate on a floor with μ = 0.4:
- N = 10 × 9.807 = 98.07 N
- Ff = 0.4 × 98.07 = 39.23 N — the force needed to keep it sliding
Typical coefficients of friction (dry, approximate)
| Surfaces | Static μs | Kinetic μk |
|---|---|---|
| Steel on steel | 0.74 | 0.57 |
| Aluminium on steel | 0.61 | 0.47 |
| Copper on steel | 0.53 | 0.36 |
| Rubber on dry concrete | 1.0 | 0.8 |
| Wood on wood | 0.25–0.5 | 0.2 |
| Glass on glass | 0.94 | 0.4 |
| Waxed ski on snow | 0.14 | 0.1 |
| PTFE on PTFE | 0.04 | 0.04 |
| Ice on ice | 0.1 | 0.03 |
Values vary widely with surface finish, contamination and lubrication — use measured values for design.
Frequently asked questions
What is the formula for friction force?
F = μ × N, where μ is the coefficient of friction and N the normal force pressing the surfaces together. On a level surface N = m × g.
What is the difference between static and kinetic friction?
Static friction is the maximum force before an object starts to slide; kinetic friction acts while it is sliding and is usually lower. That is why it takes more force to start pushing a box than to keep it moving.
Does friction depend on contact area?
For dry, rigid surfaces, no — the classical (Amontons) law says friction depends only on μ and the normal force. Tyres and soft materials deviate from this.
How do I find the coefficient of friction?
Measure the force needed to slide the object and its normal force, enter both and clear μ — μ = F ÷ N.