Work out gearbox ratio instantly with clear inputs, formula shown and shareable results.
Gear stages multiply, so the overall ratio is the product of the stage ratios. Speed divides by that ratio and torque multiplies by it. Each meshing stage costs about 2-3 percent in efficiency, so a two-stage helical gearbox delivers roughly 94 percent of the ideal output torque.
Overall ratio
i total = i1 x i2; output rpm = input rpm / i total
Torque
Output torque = input torque x i total x stage efficiencies
i total = i1 x i2; output rpm = input rpm / i total. Gear stages multiply, so the overall ratio is the product of the stage ratios.
A single mesh above about 7:1 needs a very large gear and gives poor tooth contact. Splitting the ratio keeps both gears compact and efficiency high.
This calculator takes 4 inputs: First stage ratio, Second stage ratio, Input speed, Input torque. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.