The math: 48 ft of wall × 8 ft high is 384 sq ft, minus about 51 sq ft of openings leaves 333 sq ft. Two coats is 666 sq ft, and at 350 sq ft per gallon that is 1.9 gallons — so buy two.
The ceiling is a separate 144 sq ft: one gallon of ceiling paint handles two coats with plenty left. Trim, door and window casings typically take about a quart of semi-gloss.
12×12 room paint checklist (2 coats)
| Surface | Amount |
|---|---|
| Walls | 2 gallons (7.5 L) |
| Ceiling | 1 gallon (3.8 L) |
| Trim and casings | 1 quart (1 L) |