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.
A square hectometer (often abbreviated as hm²) is a unit of area in the International System of Units (SI). It represents a square with sides that each measure 100 meters (10,000 centimeters) in length.
One square hectometer is equal to 10,000 square meters (m²) because each side of the square is 100 meters long, and when you square that length, you get 10,000 square meters.
To put it in perspective, a square hectometer is equivalent to 0.01 square kilometers (km²) because 1 square kilometer is equal to 100 hectares.
Square hectometers are not as commonly used as some other units of area, but they can be helpful for measuring large land areas, especially in some scientific and land management contexts.