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Paint Calculator
How many gallons does a room take? Walls only, with doors and windows taken out and the number of coats counted in.
280
sq ft of wall to paint
560
sq ft counting coats
1.6
gallons, exact
2
gallons to buy
How the math works
Wall area is the room's perimeter times its height. A 12 by 10 ft room with 8 ft ceilings has 44 ft of wall length, so 352 square feet of wall. A standard door takes out about 21 square feet and an average window about 15, which leaves 280 square feet to paint in this example.
One gallon of paint covers roughly 350 square feet per coat. Two coats over 280 square feet is 560 square feet of coverage, or 1.6 gallons, so buy 2. Rough or unprimed walls drink more; add a gallon if the surface is bare drywall or heavily patched.