How to use the wet and dry film thickness calculator
Coating specifications are written in dry film thickness, but the only thickness an applicator can measure while spraying is the wet film. That is why a painter works out how many mils of wet film are needed to leave the specified dry film, then checks the work with a wet film comb as the coat goes on.
Volume solids is the bridge between the two numbers. Solvent evaporates and only the solids remain, so dry film thickness equals wet film thickness times the volume solids fraction, and the required wet film equals the target dry film divided by it. Any thinner added has to be accounted for because it lowers the effective solids content of the mixed material.
Both directions are supported here. Enter a target dry film thickness to find the wet film to apply, or enter a wet film gauge reading to see what dry film it should produce. Results appear in mils and in microns, since a US specification and an imported product data sheet often use different units.
These are theoretical figures that assume an even film. Final acceptance is based on cured dry film thickness measured with an electronic gauge according to the applicable inspection standard, so confirm the required minimums and the measurement method against the coating manufacturer data sheet and the project specification.
Frequently asked questions
Wet film thickness is what sits on the surface immediately after application, and dry film thickness is what remains once the solvent has flashed off. The material left behind is the volume solids, so DFT equals WFT multiplied by the volume solids fraction, and the WFT you need equals the target DFT divided by that fraction.
Adding thinner dilutes the solids in the can. A coating with 60 percent volume solids thinned 10 percent by volume drops to roughly 54.5 percent effective solids, so a heavier wet film has to be applied to leave the same dry film behind.
US specifications and wet film gauges are normally graduated in mils, while product data sheets from European and Asian manufacturers often quote microns. One mil equals 25.4 microns, and this calculator prints both so the gauge reading and the data sheet can be checked against each other.