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Calculation Machine

Belt Length Calculator

V-belt length between two pulleys.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Belt length
58.49 in
In millimetres
1486 mm
Speed ratio
2.5:1
Wrap angle (small)
160.8°

Quick answer

Belt length combines the wrap around both pulleys and twice the centre distance.

The formula

L = 2C + π(D+d)/2 + (D−d)²/(4C)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Large pulley diameter10 in
  • Small pulley diameter4 in
  • Centre distance18 in

Result

  • Belt length58.49 in
  • In millimetres1486 mm
  • Speed ratio2.5:1
  • Wrap angle (small)160.8°

How to use the Belt Length Calculator

  1. 1Measure both pulley diameters.
  2. 2Measure the centre-to-centre distance.
  3. 3Order the nearest standard belt above the result.

Frequently asked questions

Should I round up or down?

Round to the nearest standard size and use the tensioner for adjustment.

Does wrap angle matter?

Below 120° on the small pulley, belts start slipping.

About this calculator