Paint Calculator
How much paint do you need? Enter your room size, coats, and openings.
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Paintable wall area—
Total area (incl. coats)—
Estimated cost—
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How this calculator works
It measures your wall area (room perimeter × wall height), subtracts standard sizes for each door and window, multiplies by the number of coats, and divides by a gallon’s coverage of about 350 sq ft.
Worked example — a 12 ft × 12 ft room, 8 ft walls, 2 coats:
Perimeter 48 × 8 = 384 sq ft of wall. Minus 1 door (21) + 2 windows (30) = 333 sq ft. × 2 ÷ 350 = 1.9 gallons → buy 2 gallons.
Standard openings used
Each door counts as 21 sq ft and each window as 15 sq ft. Adjust the counts if your openings are unusually large.
Frequently asked questions
How much paint for a 12×12 room?
About 2 gallons for two coats on 8-foot walls.
How many square feet does a gallon cover?
Roughly 350 sq ft per coat on a smooth, primed surface.
Planning a wall or paint project
Surface condition matters as much as area. Rough, porous, repaired, or strongly colored surfaces may need extra primer or paint. Check the coverage printed on the product you plan to use and account for trim, ceilings, openings, and a second coat where applicable.
How to use this estimate
- Measure the project in the units shown and recheck your measurements before ordering.
- Use the waste allowance as a planning buffer, not as a substitute for a detailed material takeoff.
- Compare the result with the package yield, coverage, or weight listed by your supplier.
- Prices are user-entered estimates and may change by location, product, delivery, and season.
Accuracy and limitations
Calculapedia provides educational planning estimates. It does not inspect your site, select products, guarantee quantities, or replace a contractor, engineer, architect, building official, or supplier. Confirm the final quantity and any safety or code requirements before buying or building.