Gears
Gear Ratio Calculator
Enter driver and driven tooth counts to calculate the ideal speed reduction or multiplication ratio for a simple external gear pair.
Inputs
Formula
External gear ratio
Worked example
Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.
Inputs
- Driver gear teeth
- 20 teeth
- Driven gear teeth
- 60 teeth
Result
- Speed reduction ratio
- 3 :1
Related calculators
Continue your workflow with a related calculation.
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Calculate driven gear RPM from driver RPM and the tooth counts of a simple external gear pair.
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Estimate the driven gear tooth count required to reach a target RPM from a known driver gear and speed.
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Gear Torque Ratio Calculator
Estimate ideal driven-shaft torque from input torque and driver/driven gear tooth counts.
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Gear Center Distance Calculator
Calculate center distance for two standard external spur gears from module and tooth counts.
Technical references for this calculation
Frequently asked questions
What does a 3:1 gear ratio mean?
For a simple external pair, the driver turns three revolutions for about one revolution of the driven gear, ignoring losses.
Does module affect the ratio?
No. Tooth counts set the ideal ratio. Meshing gears must still use compatible tooth geometry such as matching module and pressure angle.