By Zencalcy Editorial TeamLast reviewed About us
A gallon of interior paint covers roughly 350 square feet in one coat on a primed, smooth wall. Textured walls, deep colours and bare drywall all reduce that. This calculator takes the area you actually paint, adds the number of coats, and rounds up to whole gallons.
Gallons of paint for walls and ceilings, with coats.
Area = L × W Units = ⌈Area × (1 + waste) ÷ coverage⌉ Cost = Units × price
One gallon covers 350 sq ft per gallon. Units are rounded up because suppliers sell whole gallons, and the waste allowance covers cuts, mistakes and future repairs.
| Symbol | Meaning |
|---|---|
| L, W | Room length and width (or wall length and height). |
| A | Area to cover, in square feet. |
| w | Waste allowance as a percentage. |
| N | Number of gallons to buy, rounded up. |
Gross wall area is 416 sq ft; after 65 sq ft of openings it is 351 sq ft. Two coats need 702 sq ft of coverage, so 2.1 gallons — buy 3.
Continue with the Wallpaper Calculator, Tile Calculator, Flooring Calculator, or the Carpet Calculator — or browse more home & garden projects and all construction calculators.
About 350 sq ft per coat on smooth, primed drywall. Allow 300 sq ft for textured walls or a strong colour change.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026