Paint Calculator
How much paint do you need? Enter room size, doors, windows and coats — get gallons for walls and ceiling.
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How Much Paint Do I Need?
One gallon of interior paint covers about 350 square feet per coat. Wall area = 2 × (length + width) × height, minus roughly 21 sq ft per door and 15 sq ft per window. Multiply by the number of coats (two is standard, especially over a darker color) and divide by 350 — this calculator does it all and rounds up to purchasable gallons and quarts.
Example: a 12×15 ft room with 8 ft ceilings, one door and two windows needs about 381 sq ft × 2 coats ÷ 350 ≈ 2.2 gallons — buy two gallons and a quart. Primer counts as its own coat when covering dark walls, stains or new drywall.
Frequently Asked Questions
How much paint for a 12x12 room?
With 8 ft ceilings: walls ≈ 384 sq ft minus a door and window ≈ 348 sq ft. Two coats ≈ 696 sq ft ÷ 350 ≈ 2 gallons for walls; add ~1 gallon if painting the 144 sq ft ceiling.
Do I really need two coats?
Usually yes — one coat rarely covers evenly, and color changes (especially light over dark) almost always need two. Paint-and-primer products may manage one coat only when repainting a similar color.
How much does a gallon of paint cover?
Manufacturers rate most interior paints at 350-400 sq ft per gallon on smooth walls. Textured or porous surfaces absorb more — use 300-325 sq ft to be safe.
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