How much paint do you need for a room?
One gallon of quality interior paint covers about 350–400 square feet per coat on smooth, primed drywall (roughly 9–10 m² per litre). For a typical 12 × 12 ft bedroom with 8 ft ceilings, that works out to about 2 gallons for two coats on the walls, and roughly another gallon if you paint the ceiling too.
Coverage drops quickly on textured, porous or unprimed surfaces — budget 250–300 ft² per gallon for new drywall without primer, popcorn ceilings or rough plaster.
Tips for an accurate estimate
- Measure each wall at its widest point and use the actual ceiling height — older homes often have 9 ft or taller ceilings.
- Plan two coats for colour changes, dark colours or fresh patches. One coat is only realistic when refreshing the same colour with a high-hiding paint.
- Keep 10% overage for touch-ups, roller loading and spills. You'll want leftover paint from the same batch later.
- Trim and doors are usually painted in a separate sheen; a quart covers the casing for 3–4 doors.