A square mil is a unit of area, equal to the area of a square with sides of length one mil. A mil is one thousandth of an international inch. This unit of area is usually used in specifying the area of the cross section of a wire or cable.

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1 square mil is equal to:

• 1 millionth of a square inch (1 square inch is equal to 1 million square mils)
• 6.4516×10⁻¹⁰ square metres
• about 1.273 circular mils (1 circular mil is equal to about 0.7854 square mils). 1.273 ≈ 4/π and 0.7854 ≈ π/4.

• Circular mil
• Area of a circle