Paint Calculator
Estimate how much paint you need for any room based on dimensions and coats.
Inputs
Each door subtracts about 21 sq ft of paintable area.
Each window subtracts about 15 sq ft of paintable area.
Typical paint covers 350–400 sq ft per gallon. Check the can for exact coverage.
Enter your values to see results instantly.
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How this works
Formula
Gallons = ceil((wall area − openings) × coats ÷ coverage per gallon)
Painting a room requires knowing the total surface area of your walls and how much area a gallon of paint covers. Most interior paint covers 350–400 square feet per gallon, but check the paint can for the exact number.
To find your wall area, calculate the perimeter of the room (2 × (length + width)) and multiply by the ceiling height. Then subtract the area of doors (about 21 sq ft each) and windows (about 15 sq ft each) since you won't paint over them.
Most projects need two coats for even coverage. Multiply your paintable area by the number of coats, then divide by the coverage per gallon. Always round up — it's better to have a little extra paint for touch-ups than to run out mid-project.
Worked example
12 × 10 ft room, 8 ft ceilings, 1 door, 2 windows, 2 coats
Result
Perimeter = 44 ft, wall area = 352 sq ft. Subtract 51 sq ft of openings = 301 sq ft paintable. × 2 coats = 602 sq ft. ÷ 350 = 1.72 gal → 2 gallons needed.
Frequently asked questions
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