Mechanical calculator
Gear Ratio and Speed Calculator
Calculate output speed, rotation direction and the theoretical change in torque for a simple gear train.
Formula
Output speed = driver speed × driver teeth ÷ driven teeth
An idler gear changes rotation direction, but it does not change the ratio unless it shares a shaft with another gear.
Common mistakes
- Reversing the driver and driven gear.
- Treating an idler as though it changes the ratio.
- Forgetting that every external gear mesh reverses direction.
- Assuming gears with different pitch or module can mesh.
This is the ratio, not a gear design
The calculator does not determine tooth strength, gear compatibility, lubrication, backlash, shaft load or safe speed.