As an abbreviation for a unit of measurement, "MM" stands for "Millimeter", one-thousandth of a meter. In the Metric system, the Meter is the standard length. It is comparable to a little more than a yard, about 39 inches. One-tenth of a meter is a centimeter, and one-thousandth, as noted, is a millimeter. One thousand meters is a kilometer, about 6/10ths of a mile.
Chat with our AI personalities