Calculate gear ratio

Estimate speed and torque changes across one external gear pair.

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ToolGear Ratio Calculator
Input
Output
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Preview

How it works

Gear ratio is driven tooth count ÷ driver tooth count; output speed is input speed ÷ ratio and torque is input torque × ratio. The ideal result ignores efficiency, backlash, and bearing losses.

  • Tooth count gives the pitch ratio directly.
  • One external gear pair is modelled.

Worked example

2:1 reduction gearbox
A 40-tooth gear driven by a 20-tooth gear, motor turning at 3000rpm
Input
											Driver teeth: 20
Driven teeth: 40
Input speed rpm: 3000
Input torque newton metres: 5
Output
												Gear ratio: 2
Output speed rpm: 1500
Output torque newton metres: 10

When to use this

Gearbox stages estimate shaft speed, robotics designs select torque multiplication, and bicycle drivetrains compare sprockets.

Edge cases

  • Twice as many driven teeth gives half speed and roughly double ideal torque.
  • An idler changes direction and centre distance but not ratio magnitude.
  • Real efficiency below 100% lowers output power.