Which term is a unit of area used for sizing wires, equal to the area of a circle with diameter 0.001 inch?

• A. Coaxial cable
• B. Conductor
• C. Conductivity
• D. Circular Mil

Answer: (D)

Wire sizing uses a distinct area measure that is defined as the area of a circle whose diameter is 1 mil (0.001 inch). When the diameter is 0.001 inch, that circle is exactly one circular mil, so the area is that circular mil by definition. The actual area works out to A = π(0.0005 in)^2 ≈ 7.85×10^-7 square inches. This circular mil concept is handy because it ties cross-sectional area directly to a tiny diameter and is the standard for describing conductor sizes in electrical practice. The other terms refer to cable types or material properties rather than a cross-sectional area unit, so they don’t fit as the unit used to size wires.