What is a mil?

A mil is a unit of length equal to one thousandth (10-3) of an inch (0.0254 millimeter), used, for example, to specify the thickness of materials sold in sheets.

For comparison, a regular sheet of copy paper is approximately 4 mil in thickness.

Below is a link to an online unit conversion site for your convenience.

http://www.onlineconversion.com/length_all.htm