How much does a gallon of paint cover?

About 350–400 sq ft per coat on smooth walls. Textured or porous surfaces cover less.

Do I need one coat or two?

Two coats is standard for durable, even color — especially over a different base color or fresh drywall.

Should I buy extra paint?

Yes, keep 5–10% extra for touch-ups and to ensure a consistent dye-lot match later.

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.

Open calculator

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.