Roll Diameter Calculator
Calculate current roll diameter from core diameter, material thickness and wound length.
roll
diameter
winder
web
conveyor
thickness
winding
Input values
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Enter values and click Calculate to see results here.
Formula
D = sqrt(D_core² + (4 × L × t) / π)
Worked Example
Given: A core diameter of 150 mm, material thickness 0.2 mm, and 500 m of material wound.
Step 1: Area = 500 × 0.2 = 100,000 mm²
Step 2: D = sqrt(150² + (4 × 100,000) / π) = sqrt(22,500 + 127,324) = sqrt(149,824) = 387 mm
The roll is now 387 mm in diameter. Check it fits your machine frame.
Engineering Notes
- Measurement method: For accurate results, measure the web thickness with a micrometer. 0.01 mm error in thickness causes significant diameter error over thousands of layers.
- Winder tension: Tension compresses the material. The actual diameter may be slightly less than calculated, especially for soft materials like paper or film.
- Max roll diameter: Always check the machine's maximum roll diameter rating. Exceeding it can cause mechanical failure.
- PLC integration: Use this calculation in PLC programs to estimate roll diameter from encoder counts and material thickness input.
References
- TAPPI TIP 0404-48 — Roll diameter estimation