Pulley and Belt Length Calculator

In this calculator, there are three main sections dealing with pulleys, belts and speed. In each section, only one variable is calculated, based on the checkbox.

In the first, the driver pulley is the powered (usually by an electric motor) pulley. The driven pulley is the reactive pulley to the driver.

This may be for a drill, saw, polisher or other driven device. A larger driver pulley than driven pulley will produce higher driven than driver pulley speed. Sizes can be set for either to be calculated, but usually it is for calculation of the ratio of the two of them.

Both defaults can be manually changed and still have the ratio calculated.

Ratio calculation is the default condition. By checking the box, the program determines the information from the other two values.

The ratio is the driver pulley size diameter divided by the driven pulley size diameter.

In the second, the center to center measurement is for the positions of the pulleys.

The measurement is from the center of the driver shaft holding the driver pulley to the center of the driven shaft holding the driven pulley. The belt (usually V-belt) length is the circumference of the belt at the point the belt contacts and grips the pulleys. By checking the Set box, the other field is calculated.

In the third, the input RPM is the speed of the driver pulley (usually known from the motor speed) while the output RPM is the speed of the driven pulley. Output speed is the default variable. By checking the Set box, the other is calculated.

The minimum belt wrap angle for the driven pulley is always calculated from the other factors. It is NOT an input field. Enter any variable and click on SOLVE.

The determined factors are returned. Click on Clear Values to reset all defaults and clear the previous answers.

Select which values are variable and which are fixed, then enter your known values and select SOLVE. CLEAR ALL will reset all fields.