Paint Calculator
Estimate wall paint from room perimeter and height minus doors and windows, plus an optional ceiling, using your paint’s label coverage and number of coats.
Interactive calculator · Method PAINT-COVERAGE-1.0 · Last reviewed: 2026-11-04
Calculate your scenario
Paintable area = wall length × height − doors × door area − windows × window area + ceiling area.
Your inputs
Default worked example. Edit the inputs to calculate your scenario.
Default worked example
(48 × 8 − 50 + 0) sq ft × 2 coats ÷ 350 sq ft/gal = 1.91 gal → 2 × 1-gallon.
How to use the calculator
Add up the lengths of the walls you will paint, enter the wall height, the number and size of doors and windows, any ceiling in the same paint, the coats and the coverage printed on the can.
What the result means
A 12 × 12 ft room with 8 ft walls, one door and two windows has 334 sq ft to paint; two coats at 350 sq ft per gallon need about 1.91 gallons, so 2 gallons.
Formula and units
Paintable area = wall length × height − doors × door area − windows × window area + ceiling area. Gallons = paintable area × coats ÷ label coverage (sq ft per gallon). Containers = gallons ÷ container size (quart 0.25, gallon 1, 5 gallons), rounded up; cost = containers × price.
Worked examples
12 × 12 ft room, two coats: Total wall length (room perimeter): 48 ft; Wall height: 8 ft; Doors: 1 doors; Area of each door (example 20 sq ft): 20 sq ft; Windows: 2 windows; Area of each window (example 15 sq ft): 15 sq ft; Ceiling area in the same paint (0 to skip): 0 sq ft; Coats: 2 coats; Coverage from the can label (example 350): 350 sq ft per gallon per coat; Price per container (example $40): 40 $ each; Container size: gal.
Example result: Containers to buy: 2 × 1-gallon; Paint needed: 1.91 gal (7.22 L); Paintable area per coat: 334 sq ft; Left over after painting: 0.09 gal; Estimated paint cost: $80.00.
16 × 12 ft room plus ceiling in a 5-gallon pail: Total wall length (room perimeter): 56 ft; Wall height: 9 ft; Doors: 2 doors; Area of each door (example 20 sq ft): 21 sq ft; Windows: 3 windows; Area of each window (example 15 sq ft): 12 sq ft; Ceiling area in the same paint (0 to skip): 192 sq ft; Coats: 2 coats; Coverage from the can label (example 350): 400 sq ft per gallon per coat; Price per container (example $40): 180 $ each; Container size: 5gal.
Example result: Containers to buy: 1 × 5-gallon; Paint needed: 3.09 gal (11.7 L); Paintable area per coat: 618 sq ft; Left over after painting: 1.91 gal; Estimated paint cost: $180.00.
Limitations and common mistakes
Coverage comes from your paint’s label; texture, porous or patched surfaces, primer needs and color changes can lower it, so treat the result as an estimate, not a guarantee. Trim, doors and ceilings in a different product are not included unless you add them. Prices are your own.
Using a coverage figure for one coat and forgetting to multiply by the number of coats.
Sources and assumptions
Method PAINT-COVERAGE-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.