How paint coverage works
What the square feet per gallon figure on a paint can means, why new drywall and texture lower it, and how to turn it into gallons.
- Updated October 10, 2026
- By the Paint Gallons editorial team
- 5 min read
The short answer
The coverage on a paint can, written as square feet per gallon, is how much smooth, prepared surface one gallon covers in one coat. Manufacturers' figures for interior latex wall paint run from about 250 to 450 sq ft per gallon, and 350 to 400 is a common figure for a smooth, previously painted wall. Real walls often get less: new drywall absorbs more paint, and texture adds surface the tape measure does not see. The paint calculator starts from 400 sq ft per gallon, lets you enter the figure from your own can, and adjusts it for the surface.
Coverage is per coat. Two coats over 400 sq ft of wall need about twice the paint that one coat does, so the number of coats matters as much as the rate on the label. The estimate covers walls only; ceilings, trim and exterior siding are calculated separately.
What square feet per gallon means
A can rated at 400 sq ft per gallon should cover about 400 square feet with one coat when the paint is applied as the maker directs, on a surface prepared as the label describes. Sherwin-Williams calls that kind of figure theoretical: its paint FAQ points out that the texture of the surface and the tools you use are not factored into it. Treat the label rate as the best case for your wall, not a promise.
The figure depends on the product. Sherwin-Williams says a gallon of paint typically covers about 350 to 400 sq ft. Behr quotes 250 to 400 sq ft per gallon for its interior paints. Benjamin Moore lists 400 to 450 sq ft per gallon for Regal Select interior matte. Primer usually spreads less far: Sherwin-Williams puts a gallon of primer at about 200 to 300 sq ft. Read the number on the product you actually buy, or its technical data sheet, rather than borrowing one from another brand.
To estimate the paint for a job, multiply the paintable area by the coats and divide by the coverage. Sherwin-Williams gives a simple version: 1,000 sq ft at 400 sq ft per gallon is 2.5 gallons for one coat. For two coats it would be 5 gallons. Measure the area first; how to measure walls for paint walks through the perimeter method and the allowances for doors and windows.
Application changes the result as well. A thick-nap roller holds more paint, a sprayer loses some into the air, and a roller tray, brush and the inside of the can all keep a little. Spreading paint thinner than the label intends to make it go further gives weak, patchy coverage and usually costs you an extra coat.
Why the surface changes coverage
New drywall and bare plaster are porous. The paper face and the joint compound over the seams soak up paint at different rates, so the first coat goes further into the surface instead of building an even film. This Old House notes that porous surfaces like unpainted drywall absorb paint at a higher rate, so you will likely need more than the calculated amount, and recommends priming new drywall so the finish coats adhere and cover properly. The calculator models this by using 80% of the label rate for new drywall or plaster.
Textured walls, such as orange peel, knockdown or skip trowel, have more surface than their flat measurements suggest. Paint has to reach into the hollows and wrap the raised areas, and a thicker roller nap carries more paint to do it. Sherwin-Williams suggests having a little more than a gallon on hand for textured walls. The calculator uses 75% of the label rate for a textured or rough surface; a heavy texture can need more.
Behr makes the opposite point: you may need less paint than the upper estimate if you are painting a smooth, primed or sealed surface, or if the color change is subtle. That is the situation the label rate describes, and the calculator applies no adjustment for it.
A big color change is a different problem. The paint still spreads at its rated coverage, but it may not hide the old color in two coats. That shows up as an extra coat or a tinted primer rather than as a lower coverage figure. The guide on how many coats of paint you need covers dark-to-light changes and primer.
Coverage by surface
The table applies the calculator's surface factors to two common label rates. These are planning allowances, not product claims; if your paint's data sheet gives a specific rate for new drywall or texture, use that instead.
| Surface | Factor | Label 400 sq ft/gal | Label 350 sq ft/gal |
|---|---|---|---|
| Smooth, previously painted, similar color | 1.00 | 400 sq ft | 350 sq ft |
| New drywall or plaster | 0.80 | 320 sq ft | 280 sq ft |
| Textured or rough wall | 0.75 | 300 sq ft | 262.5 sq ft |
| Primer (typical range, Sherwin-Williams) | Separate product | 200 to 300 sq ft | 200 to 300 sq ft |
Worked example
Take a 12 × 10 ft room with 8 ft walls: 2 × (12 + 10) × 8 = 352 sq ft. It has one door, so subtract 20 sq ft and paint 332 sq ft. The walls are smooth and painted, the color is staying close, and the paint is rated at 400 sq ft per gallon. Two coats: 332 × 2 ÷ 400 = 1.66 gallons, which rounds to 1.7 gal. The 0.7 gal remainder is over half a gallon, so the calculator's can plan is 2 gallons, and the leftover 0.3 gal is useful for touch-ups.
Now suppose the room is freshly hung drywall. The effective coverage drops to 400 × 0.8 = 320 sq ft per gallon, and 332 × 2 ÷ 320 = 2.075, or 2.1 gal: 2 gallons and 1 quart, plus primer, which is a separate product with its own coverage. With a textured finish on painted walls, coverage is 400 × 0.75 = 300 sq ft per gallon, and 332 × 2 ÷ 300 = 2.21, or 2.2 gal: again 2 gallons and 1 quart.
Bigger jobs move to 5-gallon buckets. A whole floor that works out at 5.3 gal becomes one 5-gallon bucket plus 2 quarts for the 0.3 gal remainder. Enter your own room and the rate from your can in the paint calculator, and use the paint cost calculator to compare can sizes on price.