What is the clutch torque formula?

For a single friction surface: T = μ × F × r, where μ is the coefficient of friction, F is the axial clamping force (N), and r is the mean radius of the friction disc (m). For multiple friction surfaces multiply by n: T = μ × F × r × n.

What is mean friction radius?

It is the effective radius at which friction force acts. For uniform wear, r = (R_outer + R_inner) / 2. For uniform pressure, r = 2/3 × (R_outer³ − R_inner³) / (R_outer² − R_inner²); a solid disc under uniform pressure therefore uses 2/3 × R_outer.

What friction coefficient should I use?

Typical values: dry organic/paper lining on cast iron 0.30–0.40; dry sintered metal 0.25–0.35; wet paper (ATF) 0.10–0.13; wet sintered metal (oil) 0.05–0.10. Always use the manufacturer's rated value for your material pair.

How do I count friction surfaces (n)?

n equals the number of interfaces where friction occurs. A single-disc clutch with one disc clamped between a flywheel and pressure plate has n = 2 (two rubbing faces). An automotive twin-disc clutch has n = 4.

Does this formula assume uniform pressure or uniform wear?

The formula T = μ × F × r uses the mean radius you supply. If you provide the uniform-wear mean radius, the result corresponds to the uniform-wear model (more accurate for worn clutches). Use the uniform-pressure mean radius for new clutches.

Clutch Torque Calculator

Enter clamping force, friction coefficient, and mean disc radius to compute clutch torque capacity (T = μ × F × r).

Input Parameters

Clamping Force (F)

Axial force pressing the discs together

Coefficient of Friction (μ)

Mean Friction Radius (r)

Effective radius at which friction force acts: (R_o + R_i) / 2

Number of Friction Surfaces (n)

Single-disc = 2 surfaces; twin-disc = 4 surfaces

Results

Enter values and click Calculate Torque to see results.

Common Friction Coefficients

Material Pair	Dry μ	Wet μ
Organic lining / cast iron	0.30–0.40	—
Sintered metal / steel	0.25–0.35	0.05–0.10
Paper / ATF (automatic)	—	0.10–0.13
Cork / oil	—	0.15–0.25
Asbestos (legacy)	0.35–0.45	—

Summary

This tool computes the torque capacity of a friction clutch using the standard formula T = μ × F × r × n, where μ is the coefficient of friction, F is the axial clamping force, r is the mean friction radius, and n is the number of friction surfaces. It supports both single-disc and multi-disc configurations and accepts inputs in common engineering units.

How it works

Enter the clamping (axial) force applied to the clutch discs in Newtons.
Enter the coefficient of friction for your disc material pair.
Enter the mean friction radius of the disc in millimeters.
Optionally set the number of friction surfaces (n) for multi-disc clutches.
The calculator applies T = μ × F × r × n and displays torque in N·m.

Use cases

Size a dry single-plate clutch for an automotive drivetrain.
Verify multi-disc wet clutch torque capacity during gearbox design.
Check whether an existing clutch can handle a new engine torque output.
Compare torque capacity across different friction material coefficients.
Estimate spring clamping force required for a target torque rating.
Validate clutch selections in industrial conveyor and press machinery.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu