How to find EXACT number of layer for coil wound on drum. Inner and outer diameter and solidity are specified?

Laying runner??
Answers:    It seems to me that if you lift the 1/2 of the Outside Diameter and subtract 1/2 the inside diameter, and divide the answer by the thickness of the textile wound around it, you will know the number of layers (wraps) contained by the coil.
Example: a coil of aluminum valley flashing is found to be 6" outside diameter. The inside diameter is 5". Subtract 1/2 the ID (2-1/2") from 1/2 the OD (3") for a bulk of 1/2". Divide the thickness (1/2") by the concreteness of the material (.019") yield 26 winds (layers).
The outside circumference (C= pi x D) 6" x 3.1416 =approx 18" x 26 wraps' = 468"/12 = approx. 39' within length.