The millimeter (mm) is the smallest commonly used metric unit of length, equal to one-thousandth of a meter. It is widely used in engineering drawings, manufacturing tolerances, and rainfall measurements where precision matters. One millimeter equals roughly 0.0394 inches, making it ideal for describing thin materials like paper or wire.

The centimeter (cm) is a metric unit of length equal to one-hundredth of a meter, commonly used for everyday measurements around the world. It appears on rulers, in clothing sizes, and in medical records for body measurements. One centimeter is equivalent to approximately 0.3937 inches, providing a convenient scale between millimeters and meters.