How to calculate paint for a room
Add up the area of every wall, subtract doors and windows, multiply by the number of coats, and divide by the coverage printed on the can. A standard gallon of interior latex covers about 350–400 square feet per coat on smooth, primed drywall.
Worked example: 12 × 12 ft bedroom, 8 ft ceilings
2 × (12 + 12) × 8 = 384 sq ft of wall. Subtract one door (21) and two windows (30) for 333 sq ft. Two coats at 350 sq ft per gallon need 1.9 gallons, so buy 2 gallons.
Coverage by surface
| Surface | Approx. coverage per gallon |
|---|---|
| Smooth, previously painted drywall | 350–400 sq ft |
| New drywall (primed) | 300–350 sq ft |
| Textured walls or popcorn ceiling | 250–300 sq ft |
| Rough wood siding, stucco, brick | 150–250 sq ft |
When you need two coats
Plan on two coats when changing color, painting over a darker shade, or covering new drywall. A single coat can work when refreshing the same color with a high-hide paint.
Frequently asked questions
How much paint do I need for a 12x12 room?
About 2 gallons for two coats on the walls with 8 ft ceilings, after subtracting one door and two windows. Add about 0.8 gallon for two coats on the ceiling.
How many square feet does a gallon of paint cover?
Most interior paints cover 350–400 square feet per gallon on smooth surfaces. Textured and porous surfaces use more paint.
Is it cheaper to buy a gallon or quarts?
A gallon usually costs about the same as three quarts, so if you need three quarts, buy a gallon instead.
Do I need primer?
Use primer on new drywall, patched areas, stained surfaces, or when switching from a dark to a light color.