Updated July 8, 2026
The gallon math
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: add up your wall area in square feet, subtract doors and windows, then divide by 350, since one gallon of paint covers about 350 sq ft on a typical surface. Measure the perimeter (all four wall widths added together) and multiply by the ceiling height for the gross wall area, then subtract roughly 20 square feet per standard door and 15 square feet per average window.
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 |
Room-by-room gallon guide
- 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
If several rooms are getting the same color, buy in five-gallon buckets once the total crosses roughly four to five gallons; per-gallon pricing usually beats buying individual cans one room at a time.
Ceilings get their own can
Ceilings are painted separately from walls. A 12x12 ceiling is 144 square feet, so budget about half a gallon per coat. Ceiling paint is typically thicker and covers closer to 300 to 350 square feet per gallon, and it should be bought separately from the wall color rather than assumed to come out of the same bucket.
One coat or two
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 once you enter your room.
Buy one more than the math says
Round up to the next quart or gallon rather than buying the exact number the formula returns. Running out mid-wall and needing a second trip risks a color mismatch if the store mixes a slightly different batch from a different can of tint. Most unopened paint can be returned, so a little overage is safer than a shortage. See how much painting a room costs before you shop for quotes.
Get your exact gallon count
Enter your room's dimensions and coat count for a number in seconds.