Use effective material thickness
Liner, laminate, adhesive and coating can all contribute to wound thickness. Use the effective caliper of the wound construction rather than only the face film.
ROLL DIAMETER
Convert metres into
a physical roll.
Use wound-roll geometry to estimate outer diameter or material length from core diameter and effective material thickness, with the formula kept visible for inspection.
✓ Formula shown✓ Editable assumptions✓ Browser-local
Length, thickness and core
D = √(d² + 4tL/π), using consistent length units
L = π(D² − d²) / 4t
Modeled roll size
Outer diameter–mm
Material length–metres
Radial build–mm from core radius
GEOMETRIC MODEL
Enter material thickness and core.
Real rolls contain air, tension variation and thickness tolerances; use measured diameter for receiving or machine-clearance decisions.
Small thickness errors accumulate over hundreds of metres.
Core diameter is not core radius
The formula uses diameter consistently. Enter the actual outside diameter of the core that the material winds around.
Machine clearance needs margin
A mathematically predicted roll diameter should not be used exactly at a machine clearance limit. Production tolerances and winding density deserve a real safety margin.