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Belt and Pulley Ratio Calculator

Find the ratio of a simple Belt and Pulley drive with this
Belt and Pulley Ratio Calculator.

Drive Pulley Radius :
Driven Pulley Radius :

Fill in the radius of both pulleys to calculate the total ratio.
Mechanical power travels from the Drive Pulley to the Driven Pulley.


The ratio in a drive system is represented in reference to the number 1.
A ratio of 2 to 1 would be signified by 2:1. A ratio of 1/4 to one would be
signified by .25:1.

To find the total ratio, use the pulley ratio formula:


Ratio = (Radius of Driven Pulley) / (Radius of Drive Pulley)

Example: A handcrank is attached to a drive pulley of 2 inches in radius.
The belt runs from the drive pulley to a driven pulley.
The driven pulley is 6 inches in radius and is attached to a paddle that
churns butter. What is the total ratio of this belt and pulley drive?

Ratio = 6 / 2

Calculated out this gives a ratio of 3:1 . For every 3 revolutions of
the handcrank, the paddle attached to the driven pulley will move
1 revolution.