Calculate belt length, center distance, and pulley diameters for V-belt and flat belt drives. Supports open and crossed belt configurations.
Enter both pulley diameters and center distance to calculate belt length
| Type | Top Width | Thickness | V-Angle |
|---|---|---|---|
| A (4L) | 13 mm (1/2") | 8 mm | 40° |
| B (5L) | 17 mm (21/32") | 11 mm | 40° |
| C | 22 mm (7/8") | 14 mm | 40° |
| D | 32 mm (1-1/4") | 19 mm | 40° |
| E | 38 mm (1-1/2") | 23 mm | 40° |
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Belt drives are essential mechanical power transmission systems used in industrial machinery, HVAC equipment, automotive applications, and more. Our calculator determines belt length, center distance, and pulley sizing for both open and crossed belt configurations, helping you design efficient and properly tensioned belt drive systems.
Belt length calculation determines the required length of a belt to connect two pulleys at a specific center distance. The formula accounts for the arc around each pulley and the straight sections between them. Open belts have both pulleys rotating in the same direction, while crossed belts cause opposite rotation. The result uses standard belt-drive geometry — the two tangent (straight) spans plus the wrap arc around each pulley — the same open- and crossed-belt formulas used in mechanical drive design.
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In an open belt drive, both pulleys rotate in the same direction, which is the most common configuration. In a crossed belt drive, the belt crosses between pulleys causing them to rotate in opposite directions. Crossed belts have higher contact angles but experience more wear.
The minimum recommended wrap angle is typically 120 degrees. Wrap angles below this reduce belt grip and power transmission capability. If your calculated wrap angle is too low, increase center distance or use an idler pulley.
V-belt selection depends on power requirements, speed, and pulley sizes. Common sizes include A, B, C, D, and E sections. Use manufacturer power rating charts and ensure pulley groove matches belt profile. The belt length determines the specific belt number within each size.
Single-stage belt drives typically work best with speed ratios between 1:1 and 6:1. For higher ratios, consider using two-stage drives or alternative power transmission methods. Optimal efficiency is usually achieved at ratios between 1:1 and 3:1.
Yes. The open-belt formula sizes any two-pulley drive, including flat, V-belt and toothed/synchronous (timing) belts such as GT2 and HTD, as well as two-pulley conveyor belts. Enter the two pulley (or sprocket) diameters and the center distance; for timing belts, round the result to the nearest standard tooth count/pitch length.