Paint Calculator (Gallons for Walls)

Gallons of wall paint from room perimeter and height, minus doors and windows, for any number of coats.

Formula

Paintable area = perimeter × height − 20 sq ft per door − 15 sq ft per window. Gallons = area × coats ÷ label coverage.

Worked example

Inputs: Room perimeter = 48 ft; Wall height = 8 ft; Doors = 1; Windows = 2; Coats = 2; Coverage (from your can label) = 350 sq ft/gal.

Paintable sq ft	334
Gallons	1.91
Gallons to buy	2
Liters	7.22

FAQ

What coverage should I use?

Use the spread rate printed on your paint can; it varies by product and surface. 350 sq ft/gal is only a starting default.

Are the door/window deductions exact?

No. 20 and 15 sq ft are rough sizes; enter 0 and subtract your own measured openings for precision.

Sources

Geometry (volume/area formulas); no external constant needed

Drywall Calculator (Sheets Needed)

More Interior calculators

Flooring & Tile Calculator (Square Feet & Boxes)

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<p style="font-size:12px">Calculator by <a href="https://provenplaza.com/paint-calculator/">Proven Plaza</a></p>

Last reviewed 2026-10-11.