Net Wall Area Calculator
Get the true paintable wall area by subtracting doors and windows from the gross wall area — the number that drives paint and wallpaper quantities.
How it works
Gross = perimeter × height · Openings = doors × door area + windows × window area · Net = gross − openings
Paint and wallpaper are bought against the area you actually cover, so doors and windows must come off the gross wall area. Multiply the total wall run by the wall height for the gross figure, then subtract the combined area of every door and window. Some painters skip small windows to leave a natural cutting-in margin, but subtracting them gives the leaner, more accurate quantity.
Worked example
A room with 40 ft of wall at 8 ft high has 320 sq ft gross. Removing one 21 sq ft door and two 15 sq ft windows (51 sq ft total) leaves 269 sq ft of net wall to paint.
Frequently asked questions
Should I subtract doors and windows when buying paint?
For a tighter estimate, yes — especially with large openings or several windows. Many pros subtract only openings bigger than about 15 sq ft and treat small ones as free cutting-in allowance.
How do I turn net wall area into paint quantity?
Divide the net area by the coverage on the paint can (often 350–400 sq ft per gallon) and multiply by the number of coats. Round up to whole cans.
What are typical door and window sizes?
A standard interior door is about 3 × 7 ft (21 sq ft) and a common window is roughly 3 × 5 ft (15 sq ft). Adjust the per-opening areas if yours differ.
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This calculator is for educational purposes. Double-check important results before acting on them.