The gear decrease in a right-angle worm drive is dependent on the Planetary Wheel Drive number of threads or “starts” on the worm and the number of teeth on the mating worm wheel. If the worm has two starts 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 much less intuitive since it is dependent on the amount of teeth of sunlight and ring gears. The earth gears act as idlers and don't affect the apparatus ratio. The planetary equipment ratio equals the sum of the amount of teeth on the sun and ring equipment divided by the number of teeth on sunlight gear. For example, a planetary established with a 12-tooth sun gear and 72-tooth ring gear includes a gear ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear units 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 equipment and its mating gear have the same quantity of teeth, no decrease occurs and the gear ratio is 1:1. The apparatus is called an idler and its principal function is to improve the path of 
rotation instead of reduce 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) is determined by multiplying each individual gear ratio from each equipment set stage. If a gearbox contains 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 decreased to 57.5 rpm by using a 60:1 gearbox. The 10 lb-in electric electric motor torque would be risen to 600 lb-in (before efficiency losses).