Gear Design Calculator
Calculate pitch diameter, outside diameter, root diameter, and center distance for a spur gear pair from module and tooth counts.
Enter your values
Module and tooth counts for both gears in the pair.
How this calculator works
In the module system, gear geometry is defined from module (m) and tooth count (z). Pitch diameter for each gear:
Standard full-depth addendum and dedendum give outside and root diameters:
Center distance for the meshed pair is the average of the two pitch diameters, or equivalently:
Standard module reference
| Module (mm) | Typical application |
|---|---|
| 0.5 – 1 | Instruments, small mechanisms |
| 1.5 – 3 | Light machinery, gearboxes |
| 4 – 8 | Industrial power transmission |
Frequently asked questions
Does this account for profile shift or backlash?
No — this covers standard, unshifted full-depth gears. Profile-shifted gears (used to avoid undercutting on low tooth counts, or to fine-tune center distance) need additional correction factors beyond this basic geometry.
Does this work for helical gears?
This uses the standard (transverse) module for spur gears. For helical gears, use the normal module and helix angle to find the transverse module first: m_t = m_n / cos(β).