V. Ryan © 2001 - 2009

Below are examples of the way to work out 'revolutions per minute', or RPM as it is usually called.

In the example below the DRIVER gear is large than the DRIVEN gear. The general rule is - large to small gear means 'multiply' the velocity ratio by the rpm of the first gear. Divide 60 teeth by 30 teeth to find the velocity ratio. Multiply this number (2) by the rpm (120). This gives an answer of 240rpm.

If A revolves at 120 revs/min what is B ?
(Remember large gear to small gear increases revs)

In the example below the DRIVER gear is smaller than the DRIVEN gear. The general rule is - small to large gear means 'divide' the velocity ratio by the rpm of the first gear. Divide 75 teeth by 25 teeth to find the velocity ratio. divide the 60rpm by the velocity ration (3). The answer is 20rpm.

If A revolves at 60 revs/min what is B ?
(Remember small gear to large gear decreases revs)

If A revolves at 100 revs/min what is B ?

(Remember small gear to large gear decreases revs)