A square mil (abbreviated as sq mil or mil²) is a unit of area measurement used primarily in the United States for very small areas, especially in the context of electrical engineering and wire gauge measurements. One square mil is equal to one square thousandth of an inch or one square mil (0.000001 square inches).
In terms of modern metric units, one square mil is approximately equal to 6.4516 square micrometers (µm²) because there are 25.4 micrometers in one thousandth of an inch (1 mil).
Square mils are often used when specifying the cross-sectional area of wires, particularly in electrical and electronic engineering. For example, the American Wire Gauge (AWG) system uses square mils to represent the cross-sectional area of wires, with smaller wire sizes having fewer square mils, and larger wire sizes having more square mils.
The "square mile (US survey)" is a unit of area used in the United States primarily for land surveying and mapping purposes. It is different from the standard square mile, as it is based on the U.S. survey foot, which is a historical unit of length used in land surveying in the United States. The U.S. survey foot is slightly different from the international foot.
One square mile (US survey) is equal to approximately 3,097,600 square square meters (m²) or about 2.589988110336 square kilometers (km²).
This unit is used in various land-related applications, particularly in the United States, where the U.S. survey foot and the square mile (US survey) are still employed for legal and historical reasons in certain land surveys and property descriptions. It is important to be aware of the specific units being used when dealing with land measurements to avoid any discrepancies or errors.