Material calculator
Interior paint calculator
Estimate interior wall paint in gallons from the wall area and number of coats. Coverage assumes a smooth, primed surface at roughly 350 sq ft per gallon.
You'll need
2.4 gallons
Paint
- Buy (whole gallons)
- 3 gallons
What this assumes
- 400 ft² × 2 coats ÷ 350 ft²/gal, +5%.
- 350 ft²/gal is a conservative one-coat rate for a smooth, primed surface; textured or bare drywall covers less.
Coverage rates & sources
Every number this calculator uses is a published engineering constant — not an estimate we made up. Here is exactly what it assumes and where each value comes from.
- Paint coverage: ≈350 ft²/gal (one coat, smooth primed)Source: Major paint manufacturer spec sheets (Sherwin-Williams / Behr) cite 350–400 ft²/gal; we use the conservative 350
Before you buy
- Bare drywall, textured, or porous surfaces absorb more — drop coverage and/or add a primer coat.
- Deep color changes over a dark wall often need an extra coat or a tinted primer.
- Excludes ceiling and trim paint — estimate those separately.
This is a planning estimate, not a substitute for a pro's on-site measurement. For load-bearing, structural, or code-regulated work, confirm quantities with a licensed contractor.
Related calculators
- Drywall calculator — sheets, mud & tapeEstimate drywall sheets plus approximate joint compound, tape, and screws from total board area. Sheet count is solid; finishing materials vary by finish level.
- Wallpaper calculator — rollsEstimate wallpaper rolls from wall area, door/window deductions, roll coverage, and pattern waste. Wallpaper is often priced as a single roll but sold as double rolls.
- Exterior paint calculator — gallonsEstimate exterior body paint from wall area, openings, coats, and surface coverage. Rough siding and stucco cover far less per gallon than smooth primed surfaces.