Estimate paintable wall square footage and gallons needed from room dimensions, wall height, doors, windows, coats and paint coverage.
Paint estimate
Enter your measurements below. Results update automatically.
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How this calculator works
The calculator estimates the four walls of a rectangular room, subtracts typical door and window areas, then multiplies by the number of coats. Use the coverage stated on your paint can for the best estimate.
FormulaGallons = paintable wall area \u00d7 coats \u00f7 coverage per gallon
Worked example
For a 12 \u00d7 10 ft room with 8 ft walls, one door, two windows and two coats, the calculator subtracts typical opening areas before estimating gallons.
Useful answers
Paint Calculator by Square Feet FAQs
How many square feet does a gallon of paint cover?
Many interior paints quote roughly 350–400 sq ft per gallon per coat, but always use the coverage stated by the manufacturer.
Do I need two coats of paint?
Two coats are common for even colour and durability, but primer, colour change and product quality can alter the number required.
Should I subtract doors and windows?
Yes for a closer estimate. This calculator uses typical opening sizes; measure very large windows or doors separately.
Does this calculator include the ceiling?
No. Add ceiling area separately by multiplying room length by room width, then apply the number of ceiling coats and the paint coverage.