Eighteen millimeters is equal to approximately 0.70866 inches. Each millimeter is equal to 0.039370 inches. To convert between millimeters to inches, simply multiply the value in millimeters by 0.039370 to obtain the value in inches.

Millimeters are units found in the International System of Units, also known the metric system. Inches are units found in the Imperial system and the U.S. customary system of units. The metric system is widely used and is found in a majority of the countries around the world. The U.S. customary system of units is used in the United States and a few other countries.