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Gear Ratio Calculator
Compute a gear train's ratio from driver and driven gear tooth counts, then use it to find output speed (RPM) and output torque from a given input speed and torque.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Gear ratio
0:1
Output speed
0 RPM
Output torque
0 N·m
Example shown — a 4:1 reduction. Torque estimate ignores friction losses.
How it works
- Enter the tooth counts of the driver (input) and driven (output) gears.
- The tool computes the gear ratio as driven ÷ driver.
- Given your input speed and torque, output speed divides by the ratio and output torque multiplies by it (ideal case, no friction losses).
FAQ
How is the gear ratio calculated?
Gear ratio is the driven gear's tooth count divided by the driver gear's tooth count. A 48-tooth driven gear turned by a 12-tooth driver gives a 4:1 ratio — the output shaft turns once for every four turns of the input.
Why does torque increase while speed decreases?
A gear train conserves power (roughly), not speed or torque individually. When gearing down reduces output speed by a factor, it increases output torque by roughly that same factor — the classic mechanical-advantage tradeoff.
Does this account for friction losses?
No — it computes the ideal, lossless case. Real gear trains lose a few percent of power to friction and meshing losses, so actual output torque will be slightly lower than this estimate, especially in trains with multiple stages.
Ideal calculator vs. a real-world gear train
| Feature | This calculator | Real gear train |
|---|---|---|
| Instant, simple ratio math | ✓ | ✗ |
| Accounts for friction, backlash, and wear | ✗ | ✓ |
Good for a quick design estimate; for final sizing, apply your gearbox manufacturer's stated efficiency.