A square millimeter (mm²) is a unit of area measurement in the metric system. It represents the area of a square with each side measuring one millimeter in length. This unit is commonly used in fields such as engineering, architecture, and manufacturing to measure small surfaces or components. To visualize a square millimeter, imagine a tiny square that is 1 mm long on each side. Since there are 1,000,000 square millimeters in a square meter, this unit is particularly useful for measuring small areas, such as the size of a microchip or the surface area of a small piece of paper.