Our belt length calculator uses the standard engineering formula for two-pulley belt drive systems. The calculation accounts for the straight sections of belt between pulleys and the curved sections that wrap around each pulley. This formula is applicable to V-belts, serpentine belts, timing belts, and flat belts.

Understanding the Calculation

The formula breaks down into three components: the two straight sections (2C), the arc length around both pulleys (1.57(D + d)), and a correction factor for the geometry ((D - d)² / (4C)). The correction factor becomes more significant when there's a large difference in pulley sizes or a short center distance.

• Measure pulley pitch diameter for V-belts (where belt sits in groove)
• Use outer diameter for flat belts and timing belts
• Center distance should be adjustable for belt tensioning
• Minimum contact angle should be 120° on smaller pulley
• Add 2-5% to calculated length for stretch and adjustment
• Always verify with manufacturer specifications

Sources & References