SHORT ANSWER
1. The short answer
Two gallons of interior latex cover the walls of a 12×12 room with 8 ft ceilings in two coats, at the practical reference of 350 sq ft per gallon per coat. That includes normal waste and leaves a little for touch-ups.
| Scenario | Coverage needed | Practical buy |
|---|---|---|
| Walls, 2 coats | ≈ 664 sq ft | 2 gallons |
| Walls, 1 coat | ≈ 332 sq ft | 1 gallon |
| Walls + ceiling, 2 coats | ≈ 952 sq ft | 3 gallons |
| 9 ft ceilings, 2 coats | ≈ 760 sq ft | 2–3 gallons |
With one door (20 sq ft) and two windows (16 sq ft each) subtracted.
THE MATH
2. The wall math, step by step
Perimeter: 4 walls × 12 ft = 48 ft. Wall area: 48 × 8 ft = 384 sq ft. Subtract one door (about 20 sq ft) and two windows (about 16 sq ft each): 384 − 52 ≈ 332 sq ft of paintable wall.
Two coats: 332 × 2 = 664 sq ft of coverage. At 350 sq ft/gal: 664 ÷ 350 ≈ 1.9 gallons. Buy 2 — the extra margin absorbs texture and roller waste.
CEILING
3. Add the ceiling if you are painting it
A 12×12 ceiling is 144 sq ft; two coats need 288 sq ft of coverage, about 0.8 gallons — one more gallon covers ceiling plus touch-ups comfortably. Painting walls and ceiling in the same session: 3 gallons total is the practical buy.
VARIATIONS
4. Other heights, coats and paint types
Nine-foot ceilings add 48 sq ft of wall — still 2 gallons for two coats. One coat over a similar color drops the need to a single gallon. Going dark over light, or covering a flat finish with sheen? Plan the full two coats.
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