Gear Ratio & Pulley Calculator — Compound Trains and Belt Geometry
Calculate a compound gear train or solve an open belt drive for pitch length and center distance, with real downloadable diagrams and calculation tables.
Drive Workbench
Choose your inputs, or load the working example to explore the result. Your files stay on this device.
Your inputs
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Your result
Review your output, then save it to your device.
Make the next step clear.
Your findings, assumptions and next steps will appear here after you run the check.
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Explicit assumptions and supported inputs
Understand the evidence.
Focused guides explain the rules, the edge cases and the checks worth doing before you act.
Calculate a compound gear ratio correctly
Separate gear meshes from shared shafts.
Read the guide ↗Field guide / 02Use pitch diameters for belt-length calculations
Why outside diameter and nominal length can mislead.
Read the guide ↗Field guide / 03Document a drive calculation for review
Keep inputs, assumptions and component checks together.
Read the guide ↗Before you start
Can I calculate planetary gearing?
No. The stage model is a sequential fixed-axis gear train. Planetary carriers require a different kinematic model.
Does the pulley diagram include a belt purchase recommendation?
No. It reports ideal pitch length and center distance. Choose actual belt stock and adjustment using manufacturer data.
What does efficiency mean?
It is the fraction of input power transmitted by each stage. Output torque includes the efficiencies you enter.
Can I download the result?
Yes: a CSV calculation table and SVG diagram, plus the shared JSON/print report.
Sources & assumptions
Formats, algorithms and supported features are documented below. Check the stated scope and inspect your output before using it.
- Gear train calculation reference ↗
Fixed-axis simple and compound train definitions.
- Belt and pulley geometry ↗
Pitch diameters, open-belt length and wrap.
Reviewed 2026-10-17. Read our methodology or report an issue.