Roll Length Calculator
Estimate how much material (paper, film, fabric, wire, etc.) is wound onto a roll based on its diameter and thickness.
What this calculator does
The Roll Length Calculator estimates how much material — paper, plastic film, fabric, wire, tape, or similar — is wound onto a roll, using only the roll’s outer diameter, the diameter of its empty core, and the thickness of the material itself.
How the formula works
The wound material forms a solid ring (an annulus) when viewed from the end of the roll. Its cross-sectional area is π × (R² – r²), where R is the outer radius and r is the core radius. Dividing that area by the material’s thickness gives the total length, since the same volume of material is just “unrolled” into a long thin strip: Length = π × (D² – d²) ÷ (4 × thickness).
This method assumes the material is wound tightly and evenly with no air gaps. Loosely wound rolls, stretchy materials, or rolls with uneven winding will give a real length somewhat different from this estimate.
Make sure diameter and thickness are entered in the same unit system before calculating; this tool is intended for general planning and estimation purposes.