Paint Calculator
Estimate wall paint for one rectangular room with explicit dimensions, openings, coats, and product-label coverage.
One-room wall estimate: enter all four walls, total door/window area, coats, and the coverage printed on your paint label. Ceiling and trim are excluded.
One-room estimate
Paint result
- Gross wall area
- After openings
- With all coats
- Whole containers
Normalized calculation receipt
Area rounds half up to two decimals; volume rounds half up to three. Whole containers use an exact unrounded ceiling.
This is a planning estimate. Confirm dimensions, surface condition, application method, and the selected product label before buying paint.
Automatic copy was blocked. Select the current estimate below and copy it manually.
Private calculation: values stay in this tab. They are not added to the URL, history, storage, cookies, requests, or analytics. Analytics receives fixed tool, unit, package-choice, error, and action categories only.
Wall paint formula
Gross wall area = 2 × (room length + room width) × wall height. Subtract the explicit total area of doors and windows, multiply the remaining area by the number of coats, then divide by the coverage printed on the selected paint label. The calculator does not include the ceiling or hide standard door, window, coat, or coverage assumptions.
Worked example: 12 ft × 10 ft × 8 ft
Four walls have a gross area of 2 × (12 + 10) × 8 = 352 ft². Subtract 40 ft² of doors and windows to get 312 ft². Two coats cover 624 ft². At an entered label coverage of 350 ft² per U.S. gallon, the continuous estimate is 1.783 U.S. gal. With an entered 1 U.S. gal container size, the exact ratio rounds up to 2 whole containers.
Coverage, containers, and units
Sherwin-Williams describes roughly 350–400 ft² per U.S. gallon as typical coverage, while also noting that surface condition and application affect actual need. That range is explanation only: coverage remains required, blank by default, and should come from the product label you are using.
Container size is optional and has no default because packaging varies. Paint volume stays a continuous estimate rounded half up to three decimals. Whole containers are shown separately and use an exact unrounded ceiling. An exact whole ratio remains whole. This is a mathematical count, not a product-availability or purchase recommendation.
US mode uses feet, square feet, and U.S. gallons. Metric mode uses meters, square meters, and liters. NIST distinguishes U.S. and Imperial gallons; Imperial gallons are outside this calculator. Changing unit mode clears the numeric entries and restores openings to 0 and coats to 2, so existing numbers are never silently reinterpreted or converted.
Input and estimate boundaries
Enter unsigned complete ASCII decimals with up to six fractional digits. Length, width, and height must be greater than 0 and no more than 10,000. Opening area can be 0 but must be less than gross wall area and no more than 100,000,000. Coats must be a whole number from 1 to 100. Coverage and an optional container size must be greater than 0 and no more than 1,000,000. Each raw field is limited to 80 characters before ASCII spaces, tabs, carriage returns, or line feeds are trimmed.
This one-room estimate excludes ceilings, trim, floors, irregular and exterior surfaces, decks, fences, vehicles, primer, waste percentage, product catalogs, colors, price, labor, retailer availability, accounts, saved projects, and live data. Confirm measurements and label directions before purchase or application.
Frequently asked questions
How do I calculate paint for a rectangular room?
Add room length and width, multiply by two and by wall height, then subtract the total door and window area. Multiply that paintable area by the number of coats and divide by the coverage printed on your selected product label.
What paint coverage should I enter?
Use the coverage on the product label for the paint and surface you plan to use. Sherwin-Williams describes roughly 350–400 square feet per U.S. gallon as typical, but coverage varies, so this calculator has no hidden default.
Does the estimate include doors and windows?
Enter one explicit total opening area for all doors and windows you want to subtract. The calculator does not assume standard opening sizes.
How are whole paint containers calculated?
Container size is optional. When supplied, the calculator divides the exact unrounded paint volume by that size and rounds up to a whole container. This mathematical package count is separate from the continuous volume estimate.
Does this calculator include the ceiling, trim, waste, or labor?
No. It estimates wall paint for one rectangular interior room. Ceiling, trim, irregular or exterior surfaces, primer, waste, prices, labor, products, colors, and retailer availability are outside this estimate.