THE NUMORIX GUIDE
How to use the Gear Ratio Calculator
Last reviewed September 14, 2026
What this calculator does
The engine defines gear ratio as R = N_driven / N_driver.
Formula and method
The engine defines gear ratio as R = N_driven / N_driver. It then uses output RPM = input RPM / R and ideal output torque = input torque x R.
Variables and inputs
Enter driven and driver tooth counts, input RPM, and input torque. The default pair is 48 driven teeth and 16 driver teeth with 3,000 input RPM and 100 torque units; only the two tooth counts are explicitly unit-checked by the UI.
Worked example
For N_driven = 48 and N_driver = 16: R = 48/16 = 3:1. With 3,000 input RPM and 100 torque units, output RPM = 3,000/3 = 1,000 RPM and ideal output torque = 100(3) = 300 torque units.
How to interpret the result
A ratio above 1 reduces output speed and increases ideal output torque by the same factor. The result expresses the kinematic and torque tradeoff for one ideal gear pair, not the complete performance of a gearbox.
Common mistakes to avoid
Keep driven and driver in the correct positions; reversing them reverses the ratio and speed result. Do not assume the unlabeled input torque is automatically lb-ft or N*m, and do not treat ideal torque multiplication as free power.
Assumptions and limitations
The engine assumes no friction, tooth slip, backlash, bearing loss, or gear-mesh efficiency, and it does not model gear diameter, pressure angle, multi-stage layouts, or tooth strength. The UI validates positive tooth counts but does not validate RPM or torque ranges.
Practical use and checks
The Gear Ratio Calculator compares driven and driver tooth counts, then estimates output speed and ideal torque. Enter 48 driven teeth, 16 driver teeth, 3,000 input RPM, and 100 torque units as a check. The ratio should be 3:1, output speed 1,000 RPM, and ideal output torque 300 units. The slower output and larger torque are the expected tradeoff for a reduction ratio, not a gain in power. Keep the roles straight: the driver is connected to the input, and the driven gear receives motion. Reversing the tooth counts changes the ratio and can turn a reduction into a speed increase. The calculator does not assign a torque unit, so carry lb-ft or N m explicitly and do not compare unlabeled results. It assumes one ideal gear pair with no friction, backlash, tooth slip, bearing loss, mesh efficiency, gear inertia, or strength limit. A zero tooth count is invalid, and a real gear train with several stages should multiply stage ratios while accounting for each loss. Use the output as a kinematic check, then inspect speed, torque, lubrication, tooth loading, and efficiency before selecting hardware or deciding whether a gearbox can deliver the required load.