Construction
Paint Calculator
Enter your wall area or room dimensions, number of coats, and openings to estimate how many gallons of paint you'll need — based on standard coverage of about 350 square feet per gallon.
Quick answer: One gallon of paint covers about 350 sq ft per coat, so an average 12×12 room needs about 2 gallons for two coats.
- Gross wall area540 sq ft
- Doors & windows−100 sq ft
- Net paintable area440 sq ft
- Total area (2 coats)880 sq ft
- Gallons needed2.5
Based on standard coverage of 350 sq ft per gallon per coat on primed walls. Rough or porous surfaces and big color changes cover less — round up and keep a little for touch-ups.
How it works
1. Measure your wall area
Multiply the length of each wall by its height and add them together for total wall area in square feet. Subtract large openings like doors and windows. For a room, a quick estimate is the perimeter times the ceiling height.
2. Divide by paint coverage
One gallon of paint covers about 350 square feet on a smooth, primed surface (a single coat). Divide your wall area by 350 to get gallons per coat. Rough, porous, or dark-to-light surfaces cover less and may need more paint.
3. Account for coats and trim
Most jobs need two coats for even color and coverage, so double the gallons from a single-coat estimate. Add primer for new drywall or big color changes, and a separate quart or gallon for trim and doors. The calculator rounds up to whole cans.
Frequently asked questions
How much does a gallon of paint cover?
About 350 square feet per coat on smooth, primed walls. Rough or porous surfaces and bold color changes cover less and may need an extra coat.
How many coats of paint do I need?
Two coats is standard for an even finish and good durability. One coat may work when repainting a similar color; dramatic color changes can need three.
Do I subtract windows and doors?
Yes — the calculator deducts about 20 square feet per door and 15 per window so you don't over-buy. Round up to the nearest gallon at the store.
How much does a gallon of paint cover?
One gallon of interior paint covers about 350 square feet per coat on a smooth, sealed surface. Textured, porous, or previously unpainted walls absorb more and may stretch only 250 to 300 square feet per gallon. Always plan coverage per coat, then multiply by the number of coats.
How many coats of paint do I need?
Most walls need two coats for uniform color and full coverage. One coat may suffice when repainting a similar color over a sealed surface, while dramatic color changes or new drywall may need primer plus two coats. Budget paint for two coats unless you are confident one will do.
How much paint for a 12x12 room?
A standard 12-by-12 room with 8-foot ceilings has roughly 384 square feet of wall, so plan about 2 gallons for two coats. Add a quart or gallon for the ceiling and trim. This is an estimate; subtract large windows and doors for a tighter number.
Do I need primer before painting?
Use primer on new drywall, bare wood, patched areas, stained surfaces, or when making a big color change such as light over dark. Primer seals the surface so the topcoat covers evenly and may save a coat of finish paint. Painting a similar color over a clean, sealed wall usually does not require separate primer.