Gear Ratio Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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When you need a quick gear ratio check, the best result is one you can explain, not just copy. Mechanical systems combine geometry, speed, force, losses, and material limits, so a quick equation is best treated as a transparent first model. The calculator below uses a narrow equation set and shows the output in a form that is easy to sanity-check.

What this calculator does

Use the Gear Ratio Calculator when you want gear ratio from Input gear teeth number, Output gear teeth number, Input rotational speed without building a broader simulation. Supporting cards, if present, expose useful consequences of the same equation rather than introduce unrelated assumptions.

How to use it

Use measured or specified values for Input gear teeth number, Output gear teeth number, Input rotational speed, Input torque. Let the page handle supported unit conversions, but keep the physical convention consistent across the fields. If you are comparing two scenarios, change only the quantity you intend to test so the effect is easy to interpret.

How the calculation works

Gear ratio is output teeth/input teeth. Ideal output speed is input RPM divided by that ratio, while output torque is input torque multiplied by the ratio. Losses are not applied.

Example

Using the default example on the page (Input gear teeth number = 20; Output gear teeth number = 40; Input rotational speed = 1000 rpm; Input torque = 10 N·m), the calculator returns gear ratio of 2. Try increasing one input while holding the others fixed; the response should match the dependence shown in the formula above.

How to interpret the result

The gear ratio is best used as a baseline under the same operating assumptions. When comparing scenarios, keep the unit system and definition of RPM, diameter, efficiency, pressure, force, or ratio unchanged so the difference reflects the input you intended to test.

Limitations and notes

The ratio-from selector does not change the active path; tooth counts drive the headline ratio. Torque multiplication and speed reduction are ideal values that ignore mesh losses, bearing drag, compliance, and multi-stage drivetrain effects.