Dry Film Thickness (DFT) is the thickness of a coating after it is dry or fully cured. It is expressed in mils. The solids by volume property of allows you to quickly compute application DFT. 1 gallon of water spread over a 100 square foot area yields 16 wet mils. Hence, the following formula gives you the dry film thickness:
dft = 16 x (% solids by volume)
Measure a 10' x 10' (100sf) area. You may use traffic cones to mark the corners or any suitable method to mark the boundary. Spray or roll the coating while monitoring the actual consumption of product. If you run out of product before the area is fully covered, you are spraying too slowly or rolling too thick. Adjust your technique accordingly.
A toothed wet film gauge is useful for verifying application thickness while the coating is still wet.
Dry coating thickness can be checked with a non-destructive coating thickness gauge. Accuracy of these devices can be verified with a destructive thickness tester like the tooke gauge.