Material estimator

Paint Calculator

Estimate paint gallons and cost for interior walls with coats, doors, windows, ceiling option, and paint coverage.

How This Calculator Works

Paint estimates go wrong when doors, windows, coats, and ceiling area are ignored. This calculator starts with wall area and adjusts for the common variables.

Formula

Paintable area = wall area - doors - windows + optional ceiling area. Gallons = paintable area x coats / coverage per gallon, rounded up.

Assumptions

A typical gallon covers about 350-400 sq ft per coat, but rough surfaces, primer, dark color changes, and spraying can change coverage.

Example

A 12 ft by 12 ft room with 8 ft walls, one door, two windows, and two coats needs about 2 gallons when coverage is 350 sq ft per gallon.

Before You Buy

Coverage changes with surface texture, color change, primer, spraying, and paint quality.
Estimate primer separately if you are covering bare drywall, stains, strong colors, or patched surfaces.
Round up to whole gallons, but consider quarts for small trim or touch-up areas.

Common Questions

How much does one gallon cover?

Many interior paints cover about 350-400 sq ft per coat. Check the can for the exact product.

Should primer be included?

Primer is usually estimated separately because it may have different coverage and may not be needed for every project.

Why subtract doors and windows?

Doors and windows reduce paintable wall area. This calculator uses planning defaults of 21 sq ft per door and 15 sq ft per window.