Practical tools for measured work
Gear ratio and RPM calculator
Calculate driver/driven ratios, speed, torque and theoretical wheel speed with a phase diagram and chart.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Animated gear ratio
The animation uses a separate slow demonstration speed. It preserves the tooth-count ratio and direction, not the entered operating RPM. Tooth marks are schematic, not an involute mesh or a manufacturing profile.
Start and pause explicitly; changing inputs resets playback. Switching tabs or changing motion preferences pauses it. Above 120 teeth, only pitch circles and shaft markers are drawn.
External meshing gears turn in opposite directions.
Input and output speed chart
| Input rpm | Output rpm | km/h |
|---|---|---|
| 0 | 0 | 0 |
| 250 | 83.33333333 | 2.35619449 |
| 500 | 166.6666667 | 4.71238898 |
| 1000 | 333.3333333 | 9.424777961 |
| 1500 | 500 | 14.13716694 |
| 2000 | 666.6666667 | 18.84955592 |
| 3000 | 1000 | 28.27433388 |
| 4000 | 1333.333333 | 37.69911184 |
| 6000 | 2000 | 56.54866776 |
How it works
Reduction ratio = driven teeth ÷ driver teeth. Output RPM = input RPM ÷ ratio. Output torque = input torque × ratio × efficiency. Additional final-drive reduction affects wheel RPM only. Change driver rotation to inspect the angular relationship in the pitch-circle diagram.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Driver gear teeth
- 20
- Driven gear teeth
- 60
- Input speed
- 3000 rpm
- Input torque
- 10 N·m
- Transmission efficiency
- 90 %
- Driven wheel diameter
- 0.6 m
- Additional final-drive reduction
- 4
- Connection type
- External meshing gears
- Driver rotation
- 0 °
Primary result: Reduction ratio: 3.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
Integer tooth counts from 1 to 1000 are accepted as kinematic inputs, not manufacturing approval. The diagram shows pitch circles and phase, not involute teeth or an internal-gear mesh. Road speed assumes no slip and does not predict available power, traction or achievable top speed.
Frequently asked questions
What should I verify before using this result?
Recheck the physical measurements, confirm that every input uses the displayed unit, and compare the result with the applicable drawing, product specification, code requirement or test piece.
Why might the finished result differ?
Real work can include thickness, kerf, seams, tolerances, hardware allowances, installation clearances or site conditions that are outside the calculation. The limitations section identifies the main exclusions for this tool.
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