Millimeeter

Millimeter, sometimes written as millimetre depending on variant, is a unit of length in the metric system equal to one thousandth of a meter. The standard spellings are millimeter in American English and millimetre in British English and many other variants; millimeeter is not a recognized standard spelling and may be a typographical error or an informal variant.

As an SI-derived unit, the millimeter has the symbol mm. It is used for scales where measurements are too large for micrometers but too small for centimeters or meters. In decimal form, 1 mm equals 0.001 meters, and 1 meter equals 1000 millimeters. Relationships to other common units include 10 mm = 1 cm and 1000 mm = 1 m. In many technical fields, measurements are routinely reported in millimeters, with fractions often expressed to two or three decimal places.

Common applications include manufacturing tolerances, mechanical component dimensions, and thicknesses of everyday objects such as coins, plastics, and glass. In engineering and electronics, mm is frequently used for describing dimensions, gaps, and fits, while scientific contexts may use micrometers (µm) or meters depending on the scale required.

History and standardization: the millimeter arose from the metric system developed in the late 18th to early 19th centuries. Its value is defined by its relationship to the meter, the SI base unit of length. The term is universally understood in science and industry, though spelling varies by region. When precision and consistency are essential, the preferred spelling in the local standard is used.