As we all know, the electric motors have a rated RPM(revolutions per minute). If you want to get a low output rpm but the power supply is electric motor, generally, you can assemble a Speed Reducer (gearbox) for motor. How to calculate the output RPM of gearbox if coupled with motor? The following is the calculation formula.

Output RPM = Rated RPM (motor) / Reduction Ratio (speed reducer)
worm speed reducer assembled with motor
worm gearbox assembly with motor

According to the formula, an example is given.

Firstly, we know the rated RPM of the electric motor, for example, 4 poles, 1500 RPM

Secondly, we know the reduction ratio of speed reducer, for example, 15:1

Thirdly, the final output RPM of gearbox should be 100