How To Calculate Reduction Ratio

A gear-reduction ratio is calculated directly from the number of teeth on each gear. The number of teeth is a simple value to obtain and that is all you need to complete this computation. After you calculate this ratio, you can use it for any other computation you — need such as speed or torque.

Step 1

Count or obtain the number of teeth on each gear. Calculate the gear reduction ratio by dividing the second gear's number of teeth by the first gear's number.

Step 2

Reduce the resulting fraction to make it easier to read. For instance 100/75 becomes 4/3.

Step 3

Reduce your calculated ratio further to an X:1 format, which is most commonly used by calculators and equations. For example, a 4/3 ratio becomes 1.33:1.