Roof Coating Calculator
Last reviewed How we calculate
Liquid roof coatings, such as silicone, acrylic and other elastomeric products, are applied over an existing roof to seal it and reflect heat. They are sold by the gallon and applied at a rate the manufacturer specifies. This turns your roof area into an amount to buy.
Roof coating gallons and containers
Gallons and containers of roof coating for your roof area, number of coats and the product coverage rate.
This calculator needs JavaScript to work. The measurements below are the ones you would need to do the sum by hand.
Coating to order
- Containers
- Squares coated
A coating only works on a roof that is sound, clean and dry. It seals and reflects; it does not fix wet insulation, failed seams or a deck that feels soft underfoot. Most products also have minimum temperatures and dry-weather windows for application, set out on the data sheet.
How the calculation works
Coating rates are usually given in gallons per square per coat. Multiply the roof area in squares by the rate and by the number of coats, add a waste allowance for rough surfaces and spills, and divide by the container size to get the number of pails.
A worked example
A 1,250 sq ft roof is 12.5 squares. Two coats at 1.5 gallons a square each come to 37.5 gallons, and 10 percent waste brings that to 41.3 gallons, or nine 5-gallon pails.
Use the data sheet rate
The rate in the calculator is only a starting value. Coverage differs between products and between roof surfaces: a smooth single-ply membrane takes less coating than a rough granulated cap sheet or weathered asphalt, which soaks some of it up. Some products specify a dry film thickness instead, and the data sheet gives the wet rate that achieves it.
When coating is the wrong answer
A coating extends the life of a roof that is basically sound. It will not fix a deck that is soft underfoot, insulation that is already wet, or seams that have come apart, and coating over those problems hides them until they are worse. Have the roof inspected before buying the coating.
Frequently asked questions
How many coats of roof coating do I need?
Most coating systems specify two coats, and some need a primer first. The product data sheet gives the number of coats and the rate for each.
Can I coat a roof that is leaking?
Fix the leak first. A coating seals a sound surface; it will not reliably bridge an open seam or a hole, and coating over wet insulation traps the water in.
How long does a roof coating last?
It depends on the product and how thick it goes on. The manufacturer data sheet and warranty state the expected life for the thickness applied, and thicker applications usually last longer.