Belt Drive Calculator: V-Belt & Flat Belt Design Guide
Belt drives provide vibration-free, quiet power transmission with slight slip. V-belts and flat belts are widely used in fans, pumps, compressors and machine tools. This calculator accurately computes belt length, tension ratio, power capacity and centre distance.
📋 How to Use This Calculator
Select belt type, V-belt (A, B, C, D, E section) or Flat belt.
Enter driver and driven pulley diameters (mm) and centre distance.
Specify input power (kW), RPM and service factor.
View belt length, speed ratio, tensions (tight/slack side) and recommended belt quantity.
📐 Formula & Working Principle
Velocity Ratio i = D₂/D₁. Belt Length L = π(D₁+D₂)/2 + 2C + (D₂-D₁)²/(4C). Power per belt = (T₁-T₂) × v. Tension ratio T₁/T₂ = e^(μθ) (Euler's belt equation).
💡 Worked Example
V-belt drive: Driver pulley 200 mm, Driven 400 mm, C=1000 mm, n₁=1440 RPM. i=2. L=π(200+400)/2+2×1000+(400-200)²/(4×1000) = 942+2000+10 = 2952 mm ≈ B118 belt.
❓ Frequently Asked Questions
Q: How do I choose a V-belt section?
Based on design power (kW) and smaller pulley RPM, B section covers roughly 1–7.5 kW. Confirm using the belt manufacturer's selection chart.
Q: How much belt pre-tension is needed?
Too little: slipping. Too much: increased bearing load and belt wear. Deflection method: Force per mm of span = 1.5 × design power / belt speed.
Q: When should multiple V-belts be used?
When a single belt's power capacity is insufficient. Always purchase a matched set, mixing random belts causes uneven load distribution.