Updated June 17, 2026
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For a standard 12x12 room with 8-foot ceilings, plan on about 1 gallon for the first coat and 1 gallon for the second -- 2 gallons total for walls, ceiling separate. The formula is: add up your wall area in square feet, subtract doors and windows, then divide by 350 (one gallon of paint covers about 350 sq ft on a typical surface).
The paint quantity formula
Measure the perimeter of the room (add all four wall widths together) and multiply by the ceiling height. That gives your gross wall area. Subtract about 20 square feet for each standard door and 15 square feet for each average window. Divide the net area by 350 to get gallons per coat. Multiply by the number of coats you plan to apply.
Coverage per gallon by surface type
| Surface | Coverage per gallon |
|---|---|
| Smooth drywall (primed) | 350-400 sq ft |
| Textured or semi-rough wall | 300-350 sq ft |
| Rough or unpainted brick | 150-200 sq ft |
| Previously painted, good condition | 400 sq ft |
| Dark color over light (2 coats) | 175-200 sq ft effective |
Common room sizes: gallons needed
- 10x10 room (8 ft ceiling): roughly 1 gallon per coat, 2 gallons for two coats
- 12x12 room: about 1 gallon per coat, 2 gallons total
- 14x14 room: about 1.5 gallons per coat, 3 gallons total
- 12x20 living room: about 2 gallons per coat, 4 gallons total
Do not forget the ceiling
Ceilings are painted separately. A 12x12 ceiling is 144 square feet, so about half a gallon per coat. Ceiling paint is typically thicker and covers closer to 300 to 350 square feet per gallon. Buy ceiling paint separately from wall paint.
How many coats do I need?
Two coats is standard for any color change or fresh drywall. If you are repainting the same or a similar color on a surface in good condition, one coat can work. Going from light to dark or dark to light almost always needs two full coats and sometimes a primer coat first. Our paint calculator accounts for coats automatically.
Buying tip: round up one unit
Always round up to the next quart or gallon. Running out mid-wall and needing a second trip risks a color mismatch if the store mixes a slightly different batch. Most unopened paint can be returned, so overage is safer than shortage. See how much painting a room costs before you shop.
Estimate your project
Get materials and cost in seconds -- no signup needed.