Belt Tension Calculator

Work out belt tension instantly with clear inputs, formula shown and shareable results.

About Belt Tension Calculator

The useful work of a belt comes from the difference between tight and slack side tensions, Te = 33,000 x hp / belt speed. How that difference divides between the two sides is set by the capstan relation T1/T2 = e^(mu x theta), so a larger wrap angle or better grip lets the same power be carried with less total tension on the shafts.

Formulas

Effective tension

Te = 33000 x hp / belt speed fpm

Tension split

T1 / T2 = e^(mu x theta); T1 = Te x e^(mu θ) / (e^(mu θ) - 1)

Worked example

With the default values below, Belt Tension Calculator returns Effective tension of 55.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Power transmittedminimum 0.1 hp: 5 hp
Belt speedminimum 10 fpm: 3,000 fpm
Wrap angle on small pulleyminimum 30 °: 160 °
Coefficient of frictionminimum 0.05: 0.3

Results

Effective tension: 55.0 lbf
Tight side tension: 96.9 lbf
Slack side tension: 41.9 lbf
Total load on shaft: 138.9 lbf

Step by step

1Values used
2Effective tension
3Tension split
4Effective tension= 55.0 lbf
5Tight side tension= 96.9 lbf
6Slack side tension= 41.9 lbf
7Total load on shaft= 138.9 lbf

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Belt Tension figure worked out?

Te = 33000 x hp / belt speed fpm. The useful work of a belt comes from the difference between tight and slack side tensions, Te = 33,000 x hp / belt speed.

Why does over-tensioning shorten bearing life?

Total shaft load is T1 + T2. Extra tension adds nothing to transmitted power but loads the bearings directly, and bearing life falls with the cube of load.

What values do I need to enter?

This calculator takes 4 inputs: Power transmitted, Belt speed, Wrap angle on small pulley, Coefficient of friction. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.