Fixtra

Spur Gear Calculator

Core dimensions of a standard involute spur gear from module and tooth count — pitch, outside and root diameter, plus center distance and ratio for a mating pair. Standard full-depth tooth (addendum = 1·m, dedendum = 1.25·m).

Gear 1

Module (m) mm

Module = pitch diameter ÷ teeth. Imperial uses diametral pitch (DP) = teeth ÷ PD.

Number of teeth (z₁) z

Pressure angle °

Common: 20° (most modern gears) or 14.5°. Doesn't change the diameters below.

Pitch diameter—

Outside (tip) diameter—

Root diameter—

Circular pitch—

Addendum / dedendum—

Mating gear (optional)

Teeth on gear 2 (z₂) z

Same module as gear 1. Leave 0 to skip the pair.

Center distance—

Gear 2 pitch diameter—

Gear ratio (z₂ : z₁)—

PD = m · z (metric) or z / DP (imperial). OD = m(z+2), root = m(z−2.5), center distance = m(z₁+z₂)/2. For a pair to mesh, both gears need the same module and pressure angle.