Check the numbers before the model

Gear calculators for dimensions and planetary ratios

Find the module, position the shafts and understand a planetary ratio. Three free calculators put formulas, units and design limits beside results you can follow.

Choose the calculation you need

Module and diametral pitch

Find module from reference pitch diameter and tooth count, or convert between imperial DP and module.

40 mm / 20 teeth = module 2 mm

Open calculator 02

Spur gear center distance

Enter the shared module and both tooth counts. The result is the distance between shaft centers.

Module 2, 20 and 40 teeth: 60 mm

Open calculator 03

Planetary gear ratio

Choose sun teeth, ring teeth, planet count and the fixed member. Check speed and basic assembly separately.

Ring fixed, 20/60 teeth: 4:1

Open calculator

Calculate, check, then generate

Identify the geometry: check module, tooth system and units. Pitch diameter and outside diameter are different measurements.
Follow the calculation and check its assumptions. A valid number does not prove strength or interference-free tooth contact.
Pass supported module and center-distance results to the spur gear builder. Check bore, height and printing clearance there, and review the individual parts before fabrication.

Gear module guide Gear generator

Which gear geometry is supported?

Calculator	Supported geometry	Check separately
Module	Metric module, DP, standard external spur dimensions	Profile shift and helical geometry
Center distance	Two standard external spur gears with zero profile shift	Internal gears, operating mesh and printing clearance
Planetary	Simple unshifted set with equally spaced planets	Profile interference, carrier, bearings and strength