Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2004

Calculating Coating Coverage

Q. I would like to know, on behalf of Saab Aerospace/Saab Aerostructures in Sweden, if there is an easy way to calculate if you want to know roughly how much ready-to-spray paint / m2 / micron (or mil). Of course you have to calculate with a certain amount of spray loss, I guess. A plane sheet of metal has of course a higher transfer efficiency compared to a complex, machine made part.

A. Thank you for your e-mail. To calculate coverage of a coating the equation is very simple and is given below:

Coverage (ft²/gal) = 1604 ft²/gal/mil x % Volume Solids x %Transfer Efficiency
                                                                     DFT (mils)

The factor 1604 is the area that one solid gallon can cover when it is applied at a film thickness of 1 mil (0.001").

1 gal = 0.13368 ft³ = area (ft²) x thickness (ft)

1 ft = 12,000 mils

1 gal/mil = 0.133368 ft³/mil = area ft² x 1 ft
                                               12,000 mil

Area ft²/gal/mil = 0.13368 ft³/gal x 12,000 mils/ft = 1,604 ft²/gal/mil

Example:

The volume solids of a coating is 52% and the transfer efficiency of the spray application is 35%, what is the coverage if you apply the coating dry film thickness is 1.5 mil?

Coverage (ft²/gal) = 1604 ft²/gal/mil x % Volume Solids x %Transfer Efficiency
                                                                 DFT (mils)

Coverage (ft²/gal) = 1604 ft²/gal/mil x 0.52 x 0.35
                                               1.5 (mil)

= 194.5 ft²/gal

If you want to calculate the coverage in metric units the conversion factors are as follows;

1 ft = 0.3048 m
1 US gal = 3.7854 L
1 micron = 10-6 L
1 mil = 25.4 microns
1 m3 = 1,000 L
Volume solids and transfer efficiency do not have units.

Best wishes,

Ron Joseph