What is the module of a gear?

Module (m) is the ratio of pitch diameter to number of teeth: m = d/z. It defines tooth size. Standard modules per ISO 54: 0.5, 0.8, 1, 1.25, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20 mm.

How do I calculate pitch diameter?

Pitch diameter d = m × z, where m is module and z is number of teeth. Center distance a = (d1 + d2)/2 = m × (z1 + z2)/2.

What is contact stress (Hertzian stress) in gears?

Contact stress σH is the compressive stress at the tooth surface due to the contact load. ISO 6336 calculates it based on tangential force, face width, gear geometry, and elastic modulus. It determines pitting fatigue life.

What is bending stress in gear teeth?

Bending stress σF is the tensile stress at the tooth root caused by the transmitted load acting as a cantilever on the tooth. ISO 6336-3 provides the calculation method. It determines tooth breakage resistance.

How do I select gear material?

Common gear materials: Case-hardened steel (58-62 HRC, σH_lim ~1500 MPa), through-hardened steel (250-350 HB, σH_lim ~800-1200 MPa), cast iron (σH_lim ~400-600 MPa). Higher allowable stress = smaller gears.

Free Engineering Tool #094

Spur Gear Calculator

Calculate spur gear geometry and stress per ISO 6336. Enter module, teeth count, face width, and material for pitch diameter, center distance, contact and bending stress.

ISO 6336Contact StressBending Stress

Results

Pitch Diameters & Center Distance

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Contact Stress σ_H

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Bending Stress σ_F

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Tangential Force F_t

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Gear Ratio

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Tip Diameters (d_a1 / d_a2)

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Geometry

Contact Stress (simplified ISO 6336)

Bending Stress (simplified ISO 6336)

⚠️ Note: This calculator provides simplified estimates. Full ISO 6336 analysis requires additional factors (KA, KV, KHβ, KHα, ZE, ZH, ZB, YF, YS, Yε). Use for preliminary design only.

Spur Gear Calculator | ISO 6336 | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Results

Geometry

Contact Stress (simplified ISO 6336)

Bending Stress (simplified ISO 6336)