The square millimeter (mm²) is a metric unit of area equal to one-millionth of a square meter, used in precision engineering, microelectronics, and medical imaging. It is ideal for measuring the cross-sectional area of wires, the surface area of microchips, and other tiny surfaces. One square millimeter equals roughly 0.00155 square inches.

The mu (亩) is a traditional Chinese unit of area equal to approximately 666.67 square meters, used extensively in Chinese agriculture, rural land contracts, and property records. Farmland in China is almost always measured in mu, and government policies regarding grain production quotas reference this unit. One mu equals roughly 0.1647 acres or about 7,176 square feet.