Gear Ratio Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Enter Values
How to use this calculator
- Enter the number of teeth on the driver (input) and driven (output) gears.
- Optionally add the input speed and torque.
- Read the gear ratio and, if given, the output speed and torque.
How it works
The Gear Ratio Calculator divides the driven gear's teeth by the driver's: ratio = driven ÷ driver.
A ratio above 1 is a reduction — the output shaft turns slower than the input by that factor and (ignoring friction) carries proportionally more torque. Output speed = input ÷ ratio; output torque = input × ratio.
Worked example
12-tooth driver, 36-tooth driven. Ratio = 36 / 12 = 3:1. A 1500 rpm input becomes 500 rpm out, and 10 N·m becomes about 30 N·m.
Tips
- Torque gain ignores friction; real gear trains lose a few percent per stage.
Frequently asked questions
What about a multi-stage (compound) gear train?
Multiply the ratios of each stage. Two 3:1 stages give an overall 9:1. Work out each pair here and combine the results.
Can I use these results for final design?
No. These calculators are for first-pass sizing, checking and learning. They assume ideal supports, static loads and elastic behaviour, and they don't apply load factors, member capacity, buckling or connection checks. Always verify against the relevant design code (e.g. AS 4100, AS 1170, Eurocode) and have a qualified engineer sign off structural work.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.