QUICK SUMMARY
Measure the total wall area, subtract large doors and windows, divide by the coverage printed on the paint can, and multiply by the number of coats. For many projects, one gallon covers roughly 350 to 400 square feet for one coat, but the product label is the final authority.
A simple calculation
For each wall, multiply width by height. Add the wall areas together. Subtract the area of large doors and windows, then multiply the remaining area by the number of coats. Divide that total by the paint’s stated square-foot coverage.
Example
A 12-by-12-foot room with 8-foot ceilings has 384 square feet of wall area before subtracting openings: 12 × 8 × 4. If doors and windows remove about 60 square feet, the paintable area is about 324 square feet. Two coats require coverage for about 648 square feet.
Plan for the real surface
- Textured or porous walls can use more paint.
- A major color change often needs primer or an additional coat.
- Trim, ceilings, and cabinets should be calculated separately.
- Keep a small amount for future touch-ups.
Always check the coverage and application instructions for the exact primer or paint you plan to use.