Field calculator
Paint and coating coverage calculator (gallons)
Ordering paint or a protective coating comes down to the area, the number of coats, and how much area a gallon actually covers. The gallons needed equal the area times the number of coats divided by the coverage rate in square feet per gallon, plus a waste allowance. Enter the area, the coverage rate, the coats, and a waste percentage. The coverage rate is where estimates miss: the rate a manufacturer prints for a smooth surface drops sharply on rough, porous, textured, or profiled substrates, and a porous first coat soaks in far more than the coats over it, so a coating applied to a required film thickness covers less area than the ideal figure suggests. For roof and floor coatings the spec is usually a wet or dry mil thickness, which fixes the real coverage per gallon, so use the product datasheet rate for the actual surface and thickness rather than a generic number, and add waste for cutting in, touch-up, overspray, and the texture of the surface.
Result
Paint or coating quantity: gallons = area × number of coats / the coverage rate (square feet per gallon), plus a waste allowance. Enter the area, the coverage rate, the coats, and a waste percentage. The coverage rate is where estimates go wrong: the rate printed for a smooth surface drops sharply on rough, porous, textured, or profiled substrates, and a porous first coat soaks in far more than later coats, so a coating applied to a required mil thickness covers less area than the ideal number suggests. Use the product datasheet coverage for the actual surface and the specified wet or dry film thickness, and add waste for cutting in, touch-up, and overspray.
Worked example
Coating 2,000 sq ft, two coats, at 350 sq ft per gallon, with 10% waste.
- Area2,000 sq ft
- Coverage rate350 sq ft/gal
- Coats2
- Waste10%
- Base gallons = area × coats ÷ rate = 2,000 × 2 ÷ 350 = 11.4 gal.
- Add 10% waste: 11.4 × 1.10 = 12.6, round up to 13 gallons.
About 13 gallons. Porous or rough substrates drink more, so the real coverage rate is often below the label figure.
anvilfield.com/calculators/paint-coating-coverage-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Coating coverage FAQ
What is a roof restoration coating?
A roof restoration coating is a fluid-applied membrane rolled or sprayed over an aging but sound low-slope roof to renew it without a tear-off. It cures into a continuous film that seals the surface, bridges small splits, and adds reflectivity. It works only on a dry, sound substrate, not on a failed roof.
Is a roof coating restoration cheaper than a tear-off?
Yes, on a roof that qualifies. Restoration keeps the existing membrane and insulation and skips the demolition, disposal, and deck exposure, so it costs well under a tear-off. It usually does not count as a new roof layer under code either. But it does not fix wet insulation or a failed assembly, where a tear-off is the honest call.
Silicone vs acrylic roof coating: which should I use?
Use silicone on a roof that ponds or sees harsh UV, because it holds up to standing water where acrylic breaks down. Use acrylic on a roof that drains where cost and reflectivity matter, since it is cheaper and bright white but softens under standing water. Drainage and substrate choose the chemistry before price does.
Can you coat a roof with ponding water?
You can, but only with silicone, because it is not water-based and does not soften under standing water the way acrylic does. Silicone in ponding areas is usually specified thicker, often around 40 dry mils, and the warranty still governs whether ponding is covered. A coating restores the surface, not the slope.
Do you need to clean a roof before coating it?
Yes, always. A coating bonds to a clean surface, not to dirt, chalk, oil, or growth, and if the roof is dusty it sticks to the dust and peels. The standard is a manufacturer's cleaner, a power wash around 2000 psi, and a clean-water rinse, then a tape check to confirm the surface is actually clean before coating.