The gear reduction in a right-angle worm drive is dependent on the number 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 has 50 the teeth, the resulting gear ratio is 25:1 (50 / 2 = 25).
Calculating the gear ratio in a planetary gear reducer is less intuitive as it is dependent on the Planetary Wheel Drive amount of teeth of the sun and band gears. The earth gears act as idlers and do not affect the gear ratio. The planetary equipment ratio equals the sum of the amount of teeth on sunlight and ring equipment divided by the amount of teeth on sunlight gear. For example, a planetary arranged with a 12-tooth sun gear and 72-tooth ring gear has a gear ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear units can perform 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 amount of teeth, no 
reduction occurs and the apparatus ratio is 1:1. The gear is called an idler and its own principal function is to change the path of rotation rather than reduce the speed or increase the torque.
Parallel shaft gearboxes many times contain multiple gear models thereby increasing the gear reduction. The total gear decrease (ratio) depends upon multiplying each individual gear ratio from each equipment established stage. If a gearbox consists of 3:1, 4:1 and 5:1 gear sets, the total ratio is 60:1 (3 x 4 x 5 = 60). Inside our example above, the 3,450 rpm electric engine would have its acceleration decreased to 57.5 rpm by utilizing a 60:1 gearbox. The 10 lb-in electric engine torque would be risen to 600 lb-in (before effectiveness losses).