Gear Ratio Finder
Find tooth counts that hit a target gear ratio, across 1 or 2 gear stages.
Pre-filled with a common gear-set. Adjust the target ratio and hit Find Combinations.
How it works
The gear ratio of a stage comes from the tooth counts of the two gears, pulleys or sprockets. With several stages in a compound train, the stage ratios multiply:
ratio = driven teeth / driving teeth
total ratio = stage 1 ratio × stage 2 ratio
The finder tries every pair from your available values, and with 2 stages every pair of pairs. It keeps the combinations within tolerance of the target and sorts them by deviation. For flat or V-belt pulleys, enter pitch diameters instead of teeth.
Worked example. Target 3.5 with the pre-filled tooth counts. No
single pair lands within 5%: the closest, 48/15 = 3.2, is 8.6% low. Two stages
reach 20/15 × 48/18 = 3.5556, 1.6% high.
Built for machine design: gearboxes, belt and pulley stages, and chain sprockets. It does not size vehicle final drives or tire-size gearing. For idler gears and a servo drive's electronic gear ratio, see How to Calculate Gear Ratio.
Questions
How do I find the right gear ratio?
Enter a target ratio, an acceptable tolerance in percent, and a list of tooth counts or pulley diameters you have available. The Gear Finder returns every combination within tolerance, sorted by how close it lands to the target.
Does it work for pulleys and sprockets too?
Yes. Tooth counts and pulley diameters use the same math: it's a ratio of two values. The Gear Finder doesn't care whether you're matching spur gears, timing pulleys, or chain sprockets.
What tolerance should I use?
Most motion applications accept 1–3% deviation from the target ratio. Tighten below 1% if the downstream is a precision axis (printing, laser, semicon); loosen above 3% for conveyors and general transport.
Can I use 2-stage ratios?
Yes. Set max stages to 2 and the finder combines pairs from your available-values list to hit the target. Two stages cover much higher reductions than one pair can reach cleanly.
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