Calculator Inputs
Choose a solve mode, enter known values, and submit. The form uses three columns on large screens, two on smaller screens, and one on mobile.
Example Data Table
| Case | Driver Speed (RPM) | Driver Diameter (mm) | Driven Diameter (mm) | Slip (%) | Driven Speed (RPM) | Driver Belt Speed (m/s) |
|---|---|---|---|---|---|---|
| Workshop Fan Drive | 1440 | 100 | 200 | 2 | 705.60 | 7.54 |
| Pump Reduction | 960 | 125 | 250 | 3 | 465.60 | 6.28 |
| Compressor Step Down | 1750 | 80 | 160 | 1.5 | 861.88 | 7.33 |
| High Speed Step Up | 1200 | 150 | 90 | 2 | 1960.00 | 9.42 |
The example values show both speed reduction and speed increase cases for comparison.
Formula Used
Driven speed: Driven RPM = Driver RPM × (Driver Diameter ÷ Driven Diameter) × (1 − Slip ÷ 100)
Driven diameter: Driven Diameter = (Driver RPM × Driver Diameter × (1 − Slip ÷ 100)) ÷ Target Driven RPM
Driver diameter: Driver Diameter = (Target Driven RPM × Driven Diameter) ÷ (Driver RPM × (1 − Slip ÷ 100))
Driver speed: Driver RPM = (Target Driven RPM × Driven Diameter) ÷ (Driver Diameter × (1 − Slip ÷ 100))
Belt speed: Belt Speed = π × Driver Diameter in meters × Driver RPM ÷ 60
Angular velocity: ω = 2πN ÷ 60
Output power: Output Power = Input Power × Efficiency ÷ 100
Output torque: Torque = 9550 × Output Power (kW) ÷ Driven RPM
How to Use This Calculator
- Select what you want to solve: driven speed, driven diameter, driver diameter, or driver speed.
- Choose the diameter unit that matches your pulley dimensions.
- Enter all known values in the relevant fields.
- Provide belt slip if you want a more realistic output speed.
- Enter efficiency and optional input power to estimate output power and torque.
- Press the calculate button to display results below the header and above the form.
- Use the CSV or PDF buttons to save the result summary.
Frequently Asked Questions
1. What does the pulley speed calculator compute?
It computes driven speed, pulley size, input speed, speed ratio, belt speed, angular velocity, and optional output power and torque for belt-driven systems.
2. Why is slip included in the calculation?
Slip reduces actual driven speed compared with the ideal ratio. Including it makes maintenance checks, troubleshooting, and design estimates closer to real operating conditions.
3. Can this calculator handle speed reduction and speed increase?
Yes. A larger driven pulley usually reduces speed. A smaller driven pulley usually increases speed. The calculator supports both conditions automatically.
4. Which pulley diameter should I enter?
Enter the effective pulley diameter used by the belt path. Using nominal outside diameter can create small errors, especially on V-belt systems.
5. What unit should I use for pulley diameter?
Use one consistent unit for both pulleys. The calculator accepts millimeters, centimeters, meters, and inches, then converts diameter for belt speed output.
6. How accurate is the torque result?
Torque depends on correct speed, power, and efficiency inputs. It is a practical estimate for planning, not a replacement for full manufacturer drive analysis.
7. Can I use it for maintenance troubleshooting?
Yes. Compare expected speed with measured RPM to identify slip, wrong pulley size, misapplied ratios, or efficiency losses in the drive system.
8. Why are results shown above the form?
Showing results above the form keeps the answer visible immediately after submission. It also leaves export buttons near the summary for faster downloading.