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🎨Paint Calculator
How it's calculated
- Wall area = 2 × (length + width) × height
- Paintable area = wall area − doors × 21 sq ft − windows × 15 sq ft (+ length × width for the ceiling)
- Gallons = paintable area × coats ÷ coverage per gallon
We use 350 sq ft per gallon by default, the low end of the 350–400 sq ft range that paint makers quote, so you are less likely to run short. Rough or porous surfaces may need a lower number such as 250.
Paint is sold in quarts (¼ gallon), gallons and 5-gallon buckets. The suggestion below rounds up to what you can buy.
Frequently asked questions
How much does one gallon of paint cover?
About 350–400 square feet per coat on smooth, primed drywall, according to major paint makers such as Sherwin-Williams. Textured, porous or new drywall can take much more.
Do I need two coats?
Usually yes when changing color, painting over a dark color or painting new drywall. Two coats give even color and better durability.
How much paint for a 12×12 room?
With 8-foot ceilings, one door and two windows, the walls are about 333 sq ft of paintable area. Two coats at 350 sq ft per gallon is about 1.9 gallons, so buy 2 gallons.
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Last reviewed: 2026-10-17