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.
An acre (ac) is a unit of area commonly used in the United States and some other countries, especially for measuring land area, particularly in the context of real estate and agriculture.
One acre is equivalent to 43,560 square feet or 4,840 square yards. In terms of square meters, it is approximately 4,046.86 square meters.
To provide some perspective, an acre is roughly the size of a football field, excluding the end zones. It is a common unit for describing land area in rural and suburban areas, as well as for determining the size of plots of land, farms, and other land parcels.