How to use the paint quantity calculator
Paint quantity follows directly from area, target film thickness and the volume solids of the product. First find theoretical coverage, the area one gallon covers at the specified thickness, then divide the total area by that figure to get the theoretical volume of coating required.
Theoretical coverage rests on a fixed constant: a gallon of solid material spread one mil thick covers 1,604 square feet. Multiply 1,604 by the volume solids fraction and divide by the dry film thickness in mils. A coating at 60 percent volume solids applied at 2.5 mils therefore covers about 385 square feet per gallon, and halving the thickness doubles the coverage.
Ordering off the theoretical figure guarantees a shortfall, which is what the loss factor corrects. Overspray, stripe coating of edges and welds, and material left in the equipment all consume paint that never reaches the specified surface, so the practical quantity and the container count are the numbers to order against.
On protective coating work where film thickness drives corrosion performance, use the calculated quantity for procurement but remember that acceptance is decided by dry film thickness readings after cure. Check the specified minimum thickness and the manufacturer published spreading rate on the product data sheet before the order is placed.
Frequently asked questions
One gallon is 231 cubic inches. Spread at a thickness of one mil, or one thousandth of an inch, that volume covers 231,000 square inches, which is 1,604 square feet. Multiplying 1,604 by the volume solids fraction and dividing by the dry film thickness in mils gives the theoretical coverage of any coating.
It depends on the application method and the shape of the substrate. Brush and roller work commonly loses 10 to 20 percent, conventional and airless spray 20 to 40 percent, and spraying open structural steel can exceed 50 percent. Your own consumption records from similar work are the most reliable source.
Edges, welds and bolt heads receive extra stripe coats, applicators tend to spray above the minimum to stay clear of the specified thickness, and material is left in hoses, pots and containers. All of that sits on top of the theoretical volume.