Coil / Roll Stock Length

The wound material is an annulus, so L = pi (OD^2 - ID^2) / (4 t) for coil outside diameter OD, core diameter ID, and thickness t. A 48 in coil on a 16 in core at 0.024 in (24 ga) holds 5,585 ft; halve the thickness and the same coil OD holds twice the length. Exact for a tight coil with no telescoping; the last wrap and core stub trim it slightly. A layout aid; weigh or measure-off before a critical cut.

L = pi (OD^2 - ID^2) / (4 t); L_ft = L / 12.

The coil / roll stock length annulus identity, first-principles; the coil OD, core ID, and thickness come from the material.

The coil-length relation is a first-principles geometric identity (annulus cross-section = length x thickness); the coil OD, core diameter, and material thickness come from the coil.

Estimate. AHJ and licensed professional govern.

Field names used by the API: outside_diameter_in, inside_diameter_in, material_thickness_in, length_in, length_ft

• Annulus identity wound cross-section pi/4 (OD^2 - ID^2) equals unwound length x thicknessgeometry
• Tight coil assumes no air gaps or telescoping between wrapsscope of this tile
• Usable length the last wrap and core stub trim the usable length slightlyshop practice