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Gurukrupa Enterprises
Mechanical Calculators

Gear Ratio Calculator

Calculate gear ratio and output speed from driver and driven gear tooth counts.

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About this calculator

Gear ratio compares the tooth count of the driven gear to the driver gear, determining how much a gear pair increases torque or reduces speed. This calculator gives the ratio and, if driver speed is entered, the resulting output speed.

Formula

Gear Ratio = T₂ ÷ T₁, N₂ = N₁ ÷ (T₂ ÷ T₁)
  • T₁Driver gear tooth count — teeth
  • T₂Driven gear tooth count — teeth
  • N₁Driver speed — RPM
  • N₂Driven speed — RPM

Worked Example

Given: A driver gear has 20 teeth and the driven gear has 60 teeth, with the driver running at 1440 RPM.

Result: Ratio = 60 ÷ 20 = 3:1 (reduction). Output speed = 1440 ÷ 3 = 480 RPM.

How to Use

  1. Enter the number of teeth on the driver gear.
  2. Enter the number of teeth on the driven gear.
  3. Optionally enter the driver's rotational speed to also see output speed.
  4. Click Calculate.

Important Assumptions

  • Assumes a simple two-gear mesh; compound gear trains require multiplying ratios of each stage.

Common Mistakes

  • Inverting driver and driven gear teeth, which inverts the ratio.

Frequently Asked Questions

What does a 3:1 gear ratio mean?

The driven gear turns once for every three turns of the driver, reducing speed by a factor of 3 while increasing torque by the same factor (minus mechanical losses).

Does a higher gear ratio mean more torque?

Yes — for an ideal (lossless) gear pair, torque increases by the same ratio that speed decreases.

These calculators are provided for informational and estimation purposes. Results depend on the assumptions and input values used. Always verify critical engineering calculations against applicable standards, manufacturer specifications, site measurements, and qualified professional advice.