Gear Geometry Calculator | Involute Profile and Contact Ratio
Explore module, tooth counts, pressure angle and face width. View involute geometry, reference diameters, center distance and simplified contact-ratio and stress estimates under a fixed example load.
In external-gear mode, m=2mm, z1=20, z2=40, pressure angle=20° and face width=20mm give reference diameters 40.0 and 80.0mm, center distance 60.0mm and approximate bending stress 5.5MPa. Stress assumes a fixed torque of 1000N·mm (1N·m), not your own operating load.
Reference diameter d=mz and external center distance a=m(z1+z2)/2. Contact ratio is calculated from the modeled path of contact and base pitch. Stress uses approximate geometry factors, fixed torque 1000N·mm, load factors and built-in material values. It is not an ISO/AGMA rating calculation.
Questions and answers
Does increasing module alone increase contact ratio?
For geometrically similar standard external gears with unchanged tooth counts and pressure angle, the dimensionless contact ratio is unchanged. Physical dimensions increase.
Where do I enter operating torque or profile shift?
These controls are not available. Torque is fixed at 1000N·mm and the profile-shift coefficient is not an input. Do not use the stress result for a different load without an independent calculation.
Does the drawing establish that the gears can be manufactured safely?
No. Root generation, undercut, interference, tolerances and fatigue are not fully verified. Internal-gear estimates in particular need an independent geometry and interference check.
Is the Japanese version identical?
No. It currently focuses on an animated external pair and speed ratio, without these stress inputs. Check the scope on each page when switching language.