Paint Calculator
Enter your room's dimensions and how many coats you're planning. The calculator subtracts standard doors and windows and converts wall area into gallons and quarts.
Results
How the paint calculator works
Paint is estimated by coverage: one gallon of standard interior paint covers about 350 square feet per coat on a smooth, primed surface. The calculator measures your wall area (perimeter × height), subtracts standard openings — a door is about 21 sq ft, a window about 15 sq ft — and multiplies by the number of coats.
Formula: (2 × (length + width) × height − openings) × coats ÷ 350 = gallons
| Surface | Coverage |
|---|---|
| Smooth, primed drywall | 350–400 sq ft |
| Textured walls | 250–350 sq ft |
| Bare drywall / new plaster | 200–300 sq ft |
| Rough surfaces (stucco, masonry) | 150–250 sq ft |
Paint-buying tips
- Two coats is the norm — one-coat claims only hold up when repainting a similar color on a sound surface.
- Dramatic color changes (especially covering dark or red walls) often need a tinted primer plus two coats.
- Buy all gallons for one room at the same time and box (mix) them together — tint can vary slightly between cans.
- Keep a labeled quart of leftover paint for touch-ups; walls fade, so touch-up paint from years later rarely matches.
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12 × 12 ft room with 8 ft ceilings has about 384 sq ft of wall. After subtracting a door and two windows (~51 sq ft), two coats need just under 2 gallons — buy 2 gallons for walls, plus 1–2 quarts if painting the ceiling.
How much area does a gallon of paint cover?
About 350–400 sq ft per coat on smooth, primed walls. Textured or porous surfaces cut coverage to 250 sq ft or less per gallon.
Do I really need two coats of paint?
Almost always yes — two thin coats cover better, wear longer and look more even than one heavy coat. The exception is repainting the same (or very similar) color on clean walls.
Should I subtract windows and doors when measuring for paint?
Yes, if you want a tight estimate: standard doors are about 21 sq ft and windows about 15 sq ft. For rooms with only one or two openings, skipping the subtraction just builds in a small safety margin.