Dex (dx) is a unit of length equal to 116 of an inch, 0.75 line, 9 slits, or approx. 1.6 millimeters. The unit came from the shortest distance between two lines on the standard ruler. Dex can be used as an alternative to millimeter to determine the sizes of small things, such as tiny balls, brown spots on the skin, buttons on certain appliances, and insects.

Dex is a shortened and combined form of the Latin word sextus decimus and Spanish word decimosexto, both translated as sixteenth.