Quick answer
The coefficient of friction is μ = f ÷ N, the friction force divided by the normal force. A friction force of 30 N with a normal force of 100 N gives μ = 0.3.
Enter the friction force and the normal force. The calculator returns the coefficient.
Related tools: Friction Force Calculator: Friction force from the coefficient of friction and the normal force. Force Calculator: Force from mass and acceleration (Newton's second law). Centripetal Force Calculator: Force and acceleration for circular motion.
How to use the Coefficient of Friction Calculator
- Enter friction force (N) (0 or more).
- Enter normal force (N) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Friction force | A number, in N | ≥ 0 |
| Normal force | A number, in N | > 0 |
Formula and method
Formula
μ = f ÷ N
IEEE-754 double precision; shown to the decimals indicated.
Dimensionless ratio.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Friction force = 30; Normal force = 100.
| Result | Value |
|---|---|
| Coefficient of friction | 0.3 |
Example 2
Inputs: Friction force = 125; Normal force = 2500.
| Result | Value |
|---|---|
| Coefficient of friction | 0.05 |
Example 3
Inputs: Friction force = 3; Normal force = 49.03.
| Result | Value |
|---|---|
| Coefficient of friction | 0.061187 |
The first line is the headline result (coefficient of friction). IEEE-754 double precision; shown to the decimals indicated.
Reading μ
μ is dimensionless. Typical values: rubber on dry asphalt 0.7 to 0.9, wood on wood 0.25 to 0.5, steel on ice 0.03. Static friction (before sliding) is usually larger than kinetic.
Measuring it
Pull a block at constant speed with a spring scale, noting the force, then divide by its weight on a flat surface. On a slope, tan of the angle at which it starts to slide equals μ. The normal force must be positive.
How the result changes with friction force
Holding every other input at the first worked example, this table changes only friction force. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Friction force | Coefficient of friction |
|---|---|
| 15 | 0.15 |
| 30 | 0.3 |
| 60 | 0.6 |
| 120 | 1.2 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Friction force: entering "-1" shows "Friction force must be at least 0." beside that field and no result.
- Normal force: entering "0" shows "Normal force must be greater than 0." beside that field and no result.
Choosing between the Coefficient of Friction Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Friction Force Calculator](/science/friction-force-calculator/) | coefficient of friction μ and normal force | Friction force |
| [Force Calculator](/science/force-calculator/) | mass and acceleration | Force |
| [Centripetal Force Calculator](/science/centripetal-force-calculator/) | mass, speed and radius | Centripetal force |
| [Normal Force Calculator](/science/normal-force/) | mass, incline angle and gravitational acceleration | Normal force |
| [Momentum Calculator](/science/momentum-calculator/) | mass and velocity | Momentum |
Background: motion and mechanics
For constant acceleration the standard relations are v = u + at, s = ut + ½at², v² = u² + 2as and s = ½(u + v)t. Pick the equation that contains your three known quantities and the one you want. Use SI units (metres, seconds, kilograms, newtons, joules) throughout or the answer will be off by a factor.
These equations stop applying when acceleration changes during the motion, as with a rocket burning fuel; that needs calculus or numerical methods.
Assumptions and limitations
- Normal force must be positive
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for friction force and normal force to confirm this.
Frequently asked questions
Is static friction higher than kinetic?
Usually yes: it takes more force to start an object sliding (static) than to keep it sliding (kinetic).
Can μ exceed 1?
Yes, for sticky surfaces like racing tyres.
Does area matter?
Not in the basic model.
What does the Coefficient of Friction Calculator calculate?
Coefficient of friction from friction and normal forces. It returns Coefficient of friction.
What formula does the Coefficient of Friction Calculator use?
μ = f ÷ N. Dimensionless ratio.
What do I need to enter in the coefficient of Friction Calculator?
You enter Friction force (N) and Normal force (N).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Normal force must be positive.
What is an example of a coefficient of Friction result?
With friction force 30 and normal force 100, the coefficient of friction is 0.3.
Related calculators
- Friction Force Calculator — Friction force from the coefficient of friction and the normal force.
- Force Calculator — Force from mass and acceleration (Newton's second law).
- Centripetal Force Calculator — Force and acceleration for circular motion.
- Normal Force Calculator — Normal force on an object resting on a flat or inclined surface.
- Momentum Calculator — Linear momentum from mass and velocity.
- Net Force Calculator — Resultant of several forces at different angles.
- Impulse Calculator — Impulse from force and time, and the change in velocity if the mass is known.
Sources
- OpenStax, University Physics Volume 1 (Rice University): mechanics
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.