How to Paint A Room
Learn how to paint a room step by step, with the tools, materials, and a free calculator to estimate exactly what you need. To estimate paint, find the wall area (perimeter × height), subtract about 21 sq ft per door or window, multiply by the number of coats, and divide by 350 (sq ft per gallon). A 12×12 ft room with 8 ft walls needs about 2 gallons for two coats, costing roughly $50–$120.
Get exact numbers
Use the free Paint Calculator to estimate your project.
Step-by-step
- 1
Measure the walls
Add all wall lengths (perimeter) and multiply by ceiling height.
- 2
Subtract openings
Remove ~21 sq ft for each standard door or window.
- 3
Multiply by coats
Most jobs need two coats for even coverage.
- 4
Divide by coverage
One gallon covers roughly 350 sq ft per coat.
Pro tips
- Avoid: buying for one coat — Most walls need two coats for even color. Estimate for two unless you're repainting the same color over a clean surface.
- Avoid: not subtracting openings — Large windows and doors reduce the paintable area — but don't over-subtract small trim, or you'll come up short.
- Avoid: ignoring surface texture — Textured, porous, or unprimed walls drink paint and cover less than 350 sq ft per gallon. Round up.
- Avoid: skipping primer — Bare drywall and big color changes need primer — a separate product from your finish coats.