This free gear ratio calculator helps you quickly calculate the ratio between two gears from their tooth counts. It is useful during gearbox concept design and CAD layout work.
Gear Ratio Calculator
Enter both tooth counts.
Formula
Gear ratio = Driven teeth ÷ Driver teeth
A ratio greater than 1 means the driven gear has more teeth than the driver. In an ideal simplified gear pair, the driven gear rotates more slowly while providing a corresponding torque multiplication.
Example
A 20-tooth driver and 60-tooth driven gear give a ratio of 3:1. If the driver turns at 1500 RPM, the ideal driven speed is approximately 500 RPM before losses and other system effects.
Design Checks After the Ratio
Gear ratio alone is not a complete gear design. Check module or diametral pitch, center distance, tooth strength, face width, material, lubrication, backlash, alignment and transmitted torque.