Which formula is used to find circular mil area?

The term circular mil is common in expressing the cross sectional area of a wire. Electrical wires have very minute diameters that are often measured a thousandth of an inch. Hence, when you find the area of the circular wire, for convenience, the unit used is circular mil which is equivalent to one-thousandth of an inch.

For example, a wire has a diameter of 6*10⁻⁵ inches. To find its area:

A = πr² = π (6*10⁻⁵ / 2) ² = 2.83*10⁻⁹ in²

Since 1 mil = 1/1000 (inch) or 0.001 inch

A = (2.83*10⁻⁹ in²) * (1 mil / 0.001 inch) ²

A = 0.00283 circular mils