Gear Ratio Calculator
Work out what a pair of gears does to speed and torque.
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Gear Ratio Calculator by TheCalcTools
How the Gear Ratio Calculator works
Enter the tooth counts on the driver (input) and driven (output) gears, plus input speed and torque.
The ratio is driven teeth divided by driver teeth.
Speed falls by the ratio and torque rises by it, less friction losses.
The formula
Worked example
Using the default values shown in the calculator:
| Driver gear teeth | 20 |
|---|---|
| Driven gear teeth | 60 |
| Input speed (rpm) | 1800 |
| Input torque (N·m) | 10 |
| Efficiency (%) | 100 |
- Gear ratio = 60 ÷ 20 = 3.
- Output speed = 1,800 ÷ 3 = 600 rpm.
- Output torque = 10 × 3 = 30 N·m (ideal).
Result:
| Gear ratio (driven ÷ driver) | 3.000 |
|---|---|
| Output speed (rpm) | 600.0 |
| Output torque (N·m) | 30.00 |
Frequently asked questions
Which direction does the output turn?
A simple pair of external gears reverses the direction. An idler gear in between restores it.
Why does torque go up when speed goes down?
Power is torque times speed. A gear train cannot create power, so reducing speed raises torque (apart from losses).
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.