Interior Paint Quantity Calculator
Gallons needed — enter the wall area directly OR room dimensions (calculator subtracts doors/windows).
Result
How to use this calculator
- Calculate wall area (perimeter × height − doors/windows) using wall-area-for-paint.
- Enter area, coats, and coverage.
- Buy the rounded-up gallon count.
About this calculator
Interior paint coverage is typically 350-400 ft² per gallon for smooth surfaces, less for rough/textured. Two coats is standard for color changes; one coat works for same-color refresh on light colors. Always round up — running out mid-project means a return trip and possibly mismatched batch.
Frequently asked
How is coverage affected by surface?+
Two coats always?+
How much for trim and doors?+
Should I buy the cheapest paint?+
What if I have leftover paint?+
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Perimeter × ceiling height − doors and windows = paintable area.
Exterior coverage typically 250-300 ft²/gal — rougher surfaces, porous siding.
Sheets needed = wall area / sheet area (32 ft² for 4×8, 48 ft² for 4×12).
Boxes/units of flooring needed = room area / box coverage + waste.
Sheets = surface area / 32 ft² (standard 4×8 sheet) + waste.
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