What is wrap angle?
Wrap angle is how many degrees of pulley circumference the belt contacts. Lower angles reduce friction and torque capacity.
Engineering
Pulley Belt Length Calculator
Determine the total belt length required for an open belt drive with two pulleys.
Mechanical Drive Analysis
Establish belt length for consistent rotation and torque transmission.
What this calculator does
The Pulley Belt Length Calculator determines required belt length connecting two rotating pulleys. Accurate belt length is essential—undersized belts slip or break; oversized belts waste energy and increase wear.
How it works
Using the open belt formula, the calculator accounts for center distance, pulley diameters, and belt wrap geometry. It computes straight sections plus curved sections around each pulley's circumference.
Formula
Open Belt Length = 2×C + π×(D₁ + D₂)÷2 + (D₂ - D₁)²÷(4×C). Wrap angles calculated using sin(α) = |D₂ - D₁|÷(2×C). Speed ratio = D₁÷D₂.
Tips for using this calculator
- Ensure center distance meets minimum: (D₁ + D₂)÷2
- Round to nearest standard belt size available
- Larger diameter differences increase wrap angle differences
- Wrap angles less than 120° reduce belt grip significantly
- Recompute if you change center distance
Frequently asked questions
Can I use a slightly different belt length?
Slight variations (±1-2%) are acceptable with tensioning. Significant deviations reduce belt life and efficiency.
How do I know if pulleys are too close?
If center distance is less than (D₁ + D₂)÷2, pulleys are touching or overlapping geometrically. Increase spacing.