Belt Length Calculator
Calculate belt length for an open (non-crossed) two-pulley drive from pulley diameters and center distance.
Enter your values
Pulley diameters and the distance between their centers.
How this calculator works
For an open (non-crossed) belt running around two pulleys, total belt length is:
C is the center distance between pulley shafts, and D₁, D₂ are the pulley diameters (use pitch diameter for V-belts, outside diameter for flat belts). The first term accounts for the two straight belt runs, the second for the wrap around both pulleys, and the third corrects for the pulleys being different sizes.
Choosing a center distance
| Guideline | Typical range |
|---|---|
| Minimum center distance | > (D₁ + D₂) / 2 |
| Recommended range | 1 – 3 × (D₁ + D₂) |
Too short a center distance increases belt wrap angle stress and reduces belt life; too long increases whip and vibration at speed.
Frequently asked questions
Does this account for belt stretch or standard belt sizes?
No — this gives the theoretical geometric length. Round up to the nearest standard belt size from your manufacturer's catalog, and adjust center distance slightly to fit if needed.
What if the pulleys are the same diameter?
When D₁ = D₂, the correction term drops to zero and the formula simplifies to L = 2C + πD.