Belt Length Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Belt Length Calculator
Sizing a replacement or custom belt for a pulley drive system? This calculator applies the standard open belt drive length formula.
Belt Length = 2C + π(r1 + r2) + (r2 - r1)²/C
where C = center distance, r1 and r2 = pulley radii
Example
Pulleys of 100mm and 200mm diameter, 500mm center distance:
Belt Length ≈ 1,476.24 mm
How the Formula Accounts for Different Pulley Sizes
The formula combines two straight belt sections running between the pulleys, plus curved wrap sections around each pulley - when pulley sizes differ, the belt wraps a different arc length around the larger pulley than the smaller one, which the final correction term specifically captures.
Open vs. Crossed Belt Configurations
This formula assumes an open (non-crossed) belt configuration, where both pulleys rotate in the same direction - a crossed belt configuration (where pulleys rotate in opposite directions) uses a different formula, since the belt geometry between the pulleys changes significantly when the belt crosses itself.