👤 By whycalculator Team 📅 Last Updated February 27, 2026
Pulley Torque Calculator
Disclaimer: While we strive to ensure the accuracy of our calculator tools, we cannot be held responsible for any damages or financial losses resulting from their use.
When designing or analyzing a belt-driven system, knowing the actual torque available at the pulley is essential for selecting motors, shafts, and bearings correctly. Even a small error in force, radius, or efficiency can significantly affect real output performance. This Pulley Torque Calculator helps you determine the usable torque by applying the practical formula ( T= F × r × η.
Whether you’re working on industrial machinery, workshop equipment, or a custom mechanical project, this tool provides quick and reliable torque results in both N·m and lb·f
How to Calculate Pulley Torque
Pulley torque represents the rotational force produced when a belt applies a tangential force at a certain radius. In real belt-driven systems, efficiency must also be considered because mechanical losses reduce the usable output torque.
Basic Pulley Torque Formula
T = F × r × η
- T = Torque (N·m)
- F = Net tangential belt force (N)
- r = Pulley radius (meters)
- η = Efficiency (decimal form)
If you know tight-side and slack-side belt tensions, then:
F = T₁ − T₂
Where T₁ is tight-side tension and T₂ is slack-side tension.
Example
Given:
- Tight-side tension (T₁) = 500 N
- Slack-side tension (T₂) = 300 N
- Pulley radius (r) = 0.1 m
- Efficiency (η) = 95% = 0.95
Step 1: Calculate Net Force
F = 500 − 300 = 200 N
Step 2: Apply Torque Formula
T = 200 × 0.1 × 0.95
Result:
T = 19 N·m
Torque Conversion (Optional)
To convert Newton-meters (N·m) to pound-feet (lb·ft):
1 N·m = 0.737562 lb·ft
Example:
19 N·m × 0.737562 = 14.01 lb·ft
Important Notes
- Higher force increases torque.
- Larger pulley radius increases torque.
- Lower efficiency reduces usable torque.
- Always convert units properly before calculation.
Torque Formula Reference Table
| Parameter | Symbol | Formula / Unit | Description |
|---|---|---|---|
| Torque | T | N·m or lb·ft | Rotational force produced at pulley radius |
| Net Force | F | T₁ − T₂ | Difference between tight and slack belt tension |
| Pulley Radius | r | Meters (m) | Distance from center to belt contact point |
| Efficiency | η | 0 to 1 (or %) | Accounts for system losses & power loss |
| Force (N) | Radius (m) | Efficiency (%) | Torque (N·m) | Torque (lb·ft) |
|---|---|---|---|---|
| 100 | 0.05 | 90% | 4.50 | 3.32 |
| 250 | 0.10 | 95% | 23.75 | 17.53 |
| 500 | 0.15 | 92% | 69.00 | 50.90 |
| 800 | 0.20 | 90% | 144.00 | 106.19 |
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