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Wall area calculator
Gross wall area minus door and window openings — the net square footage you actually cover with drywall, paint, siding, or masonry.
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How it’s computed
Wall area = perimeter (ft) × wall height (ft) − openings (sqft). Clamped at zero — openings larger than the wall can never return a negative area.
Decimal-exact and deterministic: identical inputs always return identical results. This is the same math Ask Donnie’s estimating engine runs — not an approximation, and never a language model doing arithmetic.
Common questions
Where do I get the perimeter?
Measure the wall run directly, or use the perimeter calculator for a rectangular plan. For one wall, just use its length as the "perimeter".
How much do I subtract for a door or window?
Measure each opening. As pure arithmetic: a 3'0" × 6'8" door is about 20 sqft, a 3' × 5' window is 15 sqft — but always use your actual sizes.
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