Paint Calculator
How many gallons of paint for your room — from wall size, number of coats, and the coverage on the can.
Your project
Material estimate only — confirm quantities against your own measurements and the product packaging before you buy. Round up and keep a little extra for cuts, waste, and mistakes.
What you need
What to buy
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Wall area
— sq ft
Gallons to buy
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Est. cost
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Shopping list
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How we calculate it
wall area = 2 × (L + W) × H - openings • total = area × coats • gallons = round up( total / coverage )
Assumptions & sources
- Coverage 350–400 sq ft per gallon per coat on smooth drywall; 350 shipped as the conservative default — source: Sherwin-Williams / Behr label specs
- Textured, stucco, or brick surfaces cover less (≈220–340 sq ft/gal) — lower the coverage figure
- A standard door ≈ 20 sq ft and a window ≈ 15 sq ft if you choose to subtract openings
- Ceiling paint is calculated separately (ceiling area = length × width)
Formulas reviewed against manufacturer spec sheets and industry standards. Last verified 2026.
How to estimate paint for a room
Paint is figured from wall area: the perimeter of the room times the ceiling height gives your wall square footage. Multiply by the number of coats, divide by the coverage printed on the can (typically 350–400 sq ft per gallon on smooth drywall), and round up to whole gallons.
Getting the count right
- Two coats is normal: Most colors need two coats for even coverage — especially over a different color or fresh drywall. Plan for it unless you’re refreshing the same shade.
- Match coverage to your surface: The 350–400 sq ft/gal figure is for smooth drywall. Rough or porous surfaces drink more paint, so drop the coverage number.
- Subtracting openings is optional: For a quick estimate, skip it — painting whole then cutting in is safer than coming up short. Subtract only if you have lots of glass.
Common questions
How many gallons of paint for a 12×12 room?
With 8 ft ceilings and two coats, about 3 gallons at 350 sq ft/gal (or 2 gallons if your paint covers 400 sq ft/gal). That’s 384 sq ft of wall, 768 sq ft over two coats.
How much does a gallon of paint cover?
Typically 350–400 square feet per coat on smooth drywall. Rougher surfaces (texture, stucco, brick) cover less — as little as 220 sq ft/gal.
Do I need one coat or two?
Two is standard for full, even color. One coat may do for a same-color refresh or over a tinted primer, but new drywall and color changes almost always want two.