Paint Calculator

Methodology

Paintable area = perimeter × height − 21 sq ft per door (3×7) − 15 sq ft per window (3×5). Gallons = area × coats ÷ coverage. The default of 350 sq ft/gal suits smooth, previously painted drywall. Most manufacturer data sheets list 350–450, and textured or porous walls get 250–300 (ShedMath, paint coverage across nine data sheets, as of 2026-10-14). Retail interior paint cost about $20–$110/gal in 2026, by grade (UseCalcPro, as of 2026-10-14).

Last reviewed: 2026-10-14. Prices are national planning ranges; get local quotes.