Belt and Pulley Dimension Calculator

The pitch diameter of a pulley is not the same as the outside diameter, in fact, the pitch diameter
is very difficult to measure directly. If you cut a belt and look at the end, you will see a row of fibers near the
outside surface, the pitch diameter of any pulley is measured where these fibers contact the sheave.

Enter known or required input in mm or inches,
then click "calculate" button

Check boxes control calculated values

To calculate belt length enter size of pulleys and center to center distance.

To calculate size of one pulley enter size of second pulley and drive ratio.
Enter size of one pulley and Input and Output RPM.

To calcluate speed of driven shaft enter input RPM and size of one pulley and drive ratio
Enter input RPM and size of both pulleys.

Driver Pulley Pitch Diameter: Variable
Driven Pulley Pitch Diameter: Variable
Drive Ratio: Variable

Input RPM: Fixed
Output RPM: Fixed
minimum wrap angle:

Center to Center Distance: Fixed
Belt Length: Fixed

Belt Wrap Angle

The above drawing shows how the minimum belt wrap angle is affected by the length of the belt when a large and small pulley are used in an application. The blue belt covers more of the circumference of the smaller pulley than the red belt giving better grip on the pulley thereby allowing less slippage.

An idler is often added in situations where a short belt must be used to increase the wrap angle on a pulley.

Gear and Pulley Speed Info

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