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.
Measurement Checklist
- Measure room length, width, and wall height before subtracting doors and windows.
- Use the product label coverage for the finish paint and estimate primer separately when needed.
- Add coats for dark color changes, patched walls, porous surfaces, or uneven sheen coverage.
- Include ceilings only when the ceiling is being painted with the same coverage assumption.
Practical Examples
- 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.
- A 10 ft by 10 ft room with 8 ft walls, one door, one window, and two coats needs about 2 gallons at 350 sq ft per gallon.
- A 20 ft by 15 ft living room with 9 ft walls, two doors, three windows, ceiling included, and two coats needs about 5 gallons at 350 sq ft per gallon.
- A single 12 ft by 8 ft accent wall usually fits in 1 gallon for one coat, but textured walls and deep colors can use more.