By Zencalcy Editorial TeamLast reviewed About us
Wall area is perimeter times height, minus openings. Getting the deduction right matters: a room with two doors and three windows can lose 15–20% of the gross area, which is a whole gallon of paint.
Net wall area after doors and windows, for paint or siding.
Net area = perimeter × height − openings
A standard door is about 20 sq ft and a window 15 sq ft, but measure rather than assume. Ceilings are not included; add length × width separately if you are painting them.
| Symbol | Meaning |
|---|---|
| P | Perimeter or total wall length. |
| H | Wall height. |
| A | Net wall area. |
Perimeter 52 ft × 8 ft = 416 sq ft; deducting 45 sq ft of windows and 20 sq ft of door leaves 351 sq ft (32.6 m²).
Continue with the Gravel Calculator, Sand Calculator, Rock Calculator, or the River Rock Calculator — or browse more materials & quantities and all construction calculators.
Yes for paint and siding. Some painters ignore small openings because the trim still needs cutting in, but large glazed areas and doors should come out.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026