What is the exact thickness of the glass?

Glass thicknesses are shown as a Nominal Thickness, meaning “in name only”, used solely for identification.  These are commonly listed as 1/8″, 5/32″, 1/8″, 3/16″, 1/4″, 3/8″, and 1/2″.  The nominal size may not match the exact thickness but will be within the acceptable industry-wide thickness range and can correspond to a large number of highly standardized dimensions and tolerances.