The gear decrease in a right-angle worm drive is dependent on the amount of threads or “starts” on the worm and the number of teeth on the mating worm wheel. If the worm has two begins and the mating worm wheel offers 50 the teeth, the resulting equipment ratio is 25:1 (50 / 2 = 25).
Calculating the gear ratio in a Planetary Wheel Drive planetary equipment reducer is less intuitive as it is dependent upon the amount of teeth of the sun and band gears. The earth gears become idlers and do not affect the apparatus ratio. The planetary equipment ratio equals the sum of the amount of teeth on sunlight and ring gear divided by the number of teeth on sunlight gear. For example, a planetary arranged with a 12-tooth sun gear and 72-tooth ring gear has a equipment ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear pieces can achieve ratios from about 3:1 to about 11:1. If more equipment 
reduction is necessary, additional planetary stages may be used.
If a pinion gear and its mating gear have the same quantity of teeth, no decrease occurs and the gear ratio is 1:1. The gear is called an idler and its own major function is to change the path of rotation rather than decrease the speed or raise the torque.
Parallel shaft gearboxes many times contain multiple gear models thereby increasing the apparatus reduction. The full total gear reduction (ratio) depends upon multiplying each individual equipment ratio from each gear arranged stage. If a gearbox consists of 3:1, 4:1 and 5:1 gear units, the full total ratio is 60:1 (3 x 4 x 5 = 60). In our example above, the 3,450 rpm electric motor would have its speed reduced to 57.5 rpm by utilizing a 60:1 gearbox. The 10 lb-in electric electric motor torque would be risen to 600 lb-in (before effectiveness losses).