1 Meter = 1 000 Millimeters
There are 1000 millimeters in a meter because there are 10 decimeters in a meter, 10 centimeters in a decimeter and 10 millimeters in a centimeter, that makes 10 * 10 * 10 = 1000 mm in a meter.
Meter is a metric system base length unit and defined as the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second. It equals to 3.280839895 feet, 39.3700787 inches. The abbreviation is "m".
Millimeter is a metric length unit. It is mostly used to measure small distances in engineering and machining. The abbreviation is "mm".