Room Paint Calculator

Estimate wall-paint gallons from room dimensions, doors, windows, number of coats, and the coverage rating of the paint you plan to use.

Quick answer

Room paint quick answer

Answer: Paint quantity is based on paintable wall area, the number of coats, and the coverage rate of the paint being used.

Formula: Gallons needed = paintable square feet × coats ÷ coverage square feet per gallon, rounded up for purchasing.

Example: Coverage varies by product and surface, so the calculator keeps the coverage assumption visible and editable.

Reviewed September 1, 2026 · Methodology

Room length (ft)Room width (ft)Wall height (ft)DoorsWindowsNumber of coatsPaint coverage (sq ft / gal)Sherwin-Williams notes roughly 350–400 sq ft/gal as a common range.

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Enter your measurements and calculate.

Worked example

Example

A 12 × 12 × 8 ft room with one door, two windows, and two coats has about 666 sq ft of coated wall area. At 375 sq ft/gal that is about 1.78 gallons.

References

Sources & assumptions

Sherwin-Williams — paint calculator coverage guidance

Last reviewed September 1, 2026. Defaults are starting points; product-specific inputs are editable wherever coverage varies.

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FAQ

Common questions

How much does a gallon of paint cover?

Sherwin-Williams says a gallon typically covers about 350–400 sq ft, but product and surface conditions matter.

Does this include the ceiling?

No. This calculator estimates walls.

Why subtract doors and windows?

Those openings reduce the wall area being painted.