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CM - Circular Mil Area

The circular mil area (CM) unit denotes the cross-sectional size of a wire or a cable.

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The circular mil is a unit of area used especially when denoting the cross-sectional size of a wire or cable.

  • A circular mil is the equivalent area of a circle whose diameter is 0.001 (10-3) inch, or approximately 0.7854 millionths of a square inch.

Mils of circular wire or cable can be calculated as:

mils = 1000 d                     (1)


d = diameter of cable or wire (inches)

Example - Calculating Mil

Mils of a 1 inch wire:

mils = 1000 (1 in)

    = 1000

Mils of a 1/2 inch wire:

mils = 1000 (1/2 in)

    = 500

The Circular Mil

The circular mil area of a wire or cable is equal to its diameter - expressed in mils squared:

CM = mil2                     (2)


CM = circular mil area (CM)

The diameter in mil of a circular wire can be expressed as:

mil = CM1/2                         (2b)

Example - Calculating mil area

The mil area of an 3/8 in wire (0.375 in or 375 mil) can be calculated as

CM = (375 mils) (375 mils)

    = 140625 cmil

Example - Calculating mil

The mil of an circular wire with area 140625 CM can be calculated as

mil = 1406251/2

    = 375 mils

The Square Mil Area

The square mil is the area of a square whose sides are one mil, or 1 x 10-3 inch, and can be expressed as:

One Square Mil = (1 x 10-3)2

    = 1 x 10-6 in2

Converting Circular Mil to Square Inch

  • 1 Circular mil = 0.7854 x 10-6 Square Inch

Converting Circular Mil to Square Mil

  • 1 Circular Mil = 0.7854 Square Mil
  • 1 Square Mil = 1.27 Circular Mils

Converting Circular Mil to metric units

  • 1 circular mil = 5.066 x 10-10 m2 = 5.066 x 10-6 cm2
  • 1 m2 = 1.974 x 109 circular mil
  • 1 cm2 = 1.974 x 105 circular mil
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