Area is the number of square units needed to cover a region. The region can be any closed shape.

In the International System of Units (SI), area is commonly measured in units of square metres (m²), square centimetres (cm²), square millimetres (mm²), square kilometres (km²), etc. These units of area are derived (or compound) units in SI.

Note that although 1 m = 10 dm, 1 m² = 100 dm². [10² = 100]

In the Imperial System of Units, area (in mathematics) is commonly measured in units of square inches (in²), square feet (ft²), square yards (yd²), square miles (mi²), etc.

Note that although 1 ft = 12 in, 1 ft² = 144 in². [12² = 144]