Gear Contact Ratio Calculator

Inputs

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Specify gear tooth size by metric module or imperial diametral pitch.
Module in mm or diametral pitch in teeth per inch.
mm
Tooth count on the smaller or driving gear.
Tooth count on the mating gear.
Reference pressure angle. 20 degrees is the common modern spur-gear default.
Operating center distance. Standard unshifted center distance is m*(z1 + z2)/2.
mm
Addendum as a multiple of module. Standard full-depth external gears use 1.0.
Addendum as a multiple of module. Standard full-depth external gears use 1.0.

Results

Default result
Edit inputs
Contact ratio(epsilon_alpha)
1.635
Pass

At least one tooth pair remains in contact through the mesh.

Transverse spur-gear contact ratio.

Also computed

Path of contact(L)9.655mm

Base pitch(p_b)5.904mm

Working pressure angle(alpha_w)20°

Center distance(a)60mm

Pinion base diameter(d_b1)37.59mm

Gear base diameter(d_b2)75.18mm

Method notes 2 notes
  • This is transverse contact ratio for an external involute spur gear pair.
  • It is a geometry screen only; tooth bending stress, pitting/contact stress, backlash, tip relief, profile shift details, helix overlap and manufacturing tolerances need separate checks.

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