The square centimeter (cm²) is a metric area unit equal to one ten-thousandth of a square meter, commonly used in medical reports, lab measurements, and small product specifications. Skin lesion sizes, fabric swatches, and circuit board components are often measured in square centimeters. One square centimeter equals exactly 0.155 square inches.

The square kilometer (km²) equals one million square meters and is used to measure large land areas such as cities, national parks, and countries. Geographic data, urban planning reports, and ecological studies rely on square kilometers as their standard area unit. One square kilometer equals approximately 0.3861 square miles or about 247.1 acres.