When measuring vinyl thickness, mil is a more accurate measurement than gauge. One mil is equal to 0.001 or 1/1000 inch, while one gauge doesn't have an exact equivalent measurement.
The two units of measurement are not equal. According to actual measurement comparisons of the thickness of different vinyl pool liners, 20 mil is equal to 0.0205 inches on average, while 20 gauge is equal to 0.0185 inches. For this reason, it is recommended that consumers use mil as the reference unit when measuring and buying vinyl. In addition to being inaccurate, gauge vinyl measurement is also used differently for various products, such as wires, metal sheets, shotgun barrels and photographic films. For vinyl and photographic films, thickness increases as the gauge value increases, but for wires and metal sheets, thickness decreases as the gauge value increases.
Most suppliers sell vinyl with a thickness of 20, 27 and 30 mil. It is advantageous to choose the thicker vinyl sheets because they provide better protection against sunlight exposure and excessive use, but other factors should also be considered, such as the nature of the surface, the installer's quality of work and the degree of usage. Consider also that thicker vinyl is more expensive.