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 kilometer (km) equals 1,000 meters and is the standard unit for measuring long distances between cities, countries, and geographic features. Road signs in most countries display distances in kilometers, and running races commonly use kilometer markers. One kilometer is equivalent to about 0.6214 miles, making it easy to convert between metric and imperial distance scales.