The gear decrease in a right-angle worm drive would depend on the amount of threads or “starts” on the worm and the amount 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 apparatus ratio in a Planetary Wheel Drive Planetary equipment reducer is less intuitive as it is dependent on the number of teeth of the sun and ring gears. The planet gears become idlers and do not affect the gear ratio. The planetary gear ratio equals the sum of the amount of teeth on the sun and ring 
equipment divided by the amount of teeth on the sun gear. For instance, a planetary set with a 12-tooth sun gear and 72-tooth ring gear includes a gear ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear models can achieve ratios from about 3:1 to about 11:1. If more gear reduction is needed, additional planetary stages can be used.
If a pinion gear and its mating equipment have the same number of teeth, no reduction occurs and the gear ratio is 1:1. The apparatus is named an idler and its own major function is to change the direction of rotation rather than reduce the speed or boost the torque.
Parallel shaft gearboxes often contain multiple gear sets thereby increasing the gear reduction. The full total gear decrease (ratio) is determined by multiplying each individual gear ratio from each equipment established stage. If a gearbox includes 3:1, 4:1 and 5:1 gear units, the total ratio is 60:1 (3 x 4 x 5 = 60). In our example above, the 3,450 rpm electric motor would have its rate reduced to 57.5 rpm by using a 60:1 gearbox. The 10 lb-in electric engine torque would be risen to 600 lb-in (before efficiency losses).