What this calculator does
This tool calculates the paintable or coverable square footage of a wall, subtracting standard door and window openings, useful for estimating paint, drywall, or siding material.
The formula
Gross area = total wall length × wall height. Each standard door opening is estimated at about 21 square feet (3 ft × 7 ft) and each standard window at about 15 square feet (3 ft × 5 ft). Net area = gross area minus total opening area.
For non-standard door or window sizes, measure your actual openings and adjust your material order accordingly. This calculator uses typical residential sizes as a starting estimate.
Last reviewed August 2026