What is a worm gear and when is it used?

A worm gear consists of a worm (screw) meshing with a worm wheel (gear). Used for high reduction ratios (5:1 to 100:1) in a single stage, compact right-angle drives, and applications requiring self-locking (hoists, conveyors).

What determines worm gear efficiency?

Efficiency depends mainly on lead angle (γ) and friction coefficient (μ). η = tan(γ)/tan(γ+ρ) where ρ=arctan(μ). Higher lead angles (more starts) give better efficiency. Single-start: 40-65%, double-start: 60-80%, quad-start: 75-92%.

What is self-locking in worm gears?

Self-locking occurs when the worm wheel cannot drive the worm — the friction angle exceeds the lead angle (ρ > γ). This typically happens when efficiency is below ~50%. Useful for hoists and holding loads, but generates significant heat.

How do I calculate worm gear ratio?

Gear ratio i = Z2/z1, where Z2 is the number of worm wheel teeth and z1 is the number of worm starts. For a single-start worm with a 40-tooth wheel: i = 40/1 = 40:1.

What is the lead angle of a worm?

Lead angle γ = arctan(z1×m / d1), where z1 is number of starts, m is axial module, and d1 is worm reference diameter. Higher lead angle = better efficiency but no self-locking.

Free Engineering Tool #096

Worm Gear Calculator

Design worm gear drives. Enter module, worm starts, wheel teeth, and speed to calculate ratio, efficiency, lead angle, and self-locking check. Efficiency typically 50–90%.

Worm DriveSelf-LockingEfficiency

Results

Gear Ratio & Efficiency

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Lead Angle (γ)

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Self-Locking

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Output Speed

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Wheel Pitch Diameter

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Center Distance

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Gear Ratio

Lead Angle

Efficiency

Self-locking occurs when γ < ρ (friction angle), i.e., efficiency < ~50%.

Starts	Typical Lead Angle	Typical Efficiency	Self-Locking?
1	2–6°	40–65%	Usually yes
2	6–12°	60–80%	Sometimes
3	10–18°	70–85%	Rarely
4	14–25°	75–92%	No

Worm Gear Calculator | Efficiency & Self-Locking | Free Online Tool

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

Results

Gear Ratio

Lead Angle

Efficiency