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Paint Calculator: How Much Paint Do I Need? (Gallons)

Enter your room size in feet, doors, windows and coats to see how many gallons and quarts of wall, ceiling and trim paint to buy.

Tool inputs stay in your browser · optional AI search sends your query

Good to know: Scope: how many gallons and quarts of paint to buy for the walls of a room (or any wall area you already know in square feet), with an optional ceiling and trim, in US units. It follows the BEHR method: wall area = room perimeter × wall height, minus about 20 square feet for each door and 15 square feet for each window; the ceiling is length × width; trim is its total length × 0.5 ft (a 6-inch average width). One gallon covers 250 to 400 square feet with one coat, so paint = area × coats ÷ coverage, rounded up to whole quarts (4 quarts = 1 gallon, NIST Handbook 44). The number of coats is your choice. Not included: exterior gables, siding, decks, fences, stain, spray equipment, primer quantities (check the primer label), the paint lost in rollers and trays, prices in your area and sales tax. Everything stays in this browser tab; nothing is sent or saved. Independent ToolsKo estimate, not a paint maker’s calculator. Sources reviewed November 11, 2026.

How to use it (step by step)

  1. 1Measure the room’s length and width and the wall height in feet (or pick “I know the wall square feet”), then count the doors and windows.
  2. 2Choose how many coats, the kind of surface (smooth walls cover more than rough or unpainted ones) or type the coverage printed on your paint can, and whether you are painting the ceiling too.
  3. 3Read the gallons and quarts to buy. Add the trim length if you are painting baseboards and door or window frames, and round up if your walls are rough or the color change is big.

Words to know

Coverage
How many square feet one gallon paints with one coat. It is printed on the can, often 250 to 400 square feet.
Coat
One full layer of paint over the whole surface. Two coats use twice as much paint as one.
Perimeter
The distance all the way around the room: 2 × (length + width). A 12 × 12 ft room has a 48 ft perimeter.
Trim
Baseboards, crown molding and the frames around doors and windows, usually painted with a separate can.

Explore tools for Australia, the US & Europe →

Sources & methods

References checked November 11, 2026. Read each tool’s scope and assumptions before relying on its result.

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