To calculate the area of a circle in circular mils, which formula is used?

The area of a circle is typically calculated using the formula A = πr², where r represents the radius. However, when calculating the area in circular mils, the formula is adapted to involve the diameter (d) of the circle.

The correct formula for calculating the area of a circle in circular mils is πd². This is because circular mils is a unit of area used in electrical applications, particularly for determining the cross-sectional area of conductors. A circular mil is defined as the area of a circle with a diameter of one mil (one-thousandth of an inch).

By using the diameter in the formula πd², you can accurately calculate the area in terms of circular mils, which simplifies engineering calculations for wire sizes and their respective capacities. Using the diameter directly allows for a straightforward conversion into the area measurement needed for electrical applications.

In contrast, using just the radius (which appears in the second option) does not directly account for circular mils, while the other two options provide incomplete representations of area calculations. Hence, πd² is the most appropriate selection for this specific area calculation.