How Much Paint Do You Need for a Room?

Published 2026-02-02

To find paint for a room, multiply the room perimeter by the wall height for total wall area, subtract doors and windows, then divide by 350 sq ft per gallon and multiply by the number of coats. A 12 × 12 ft room with 8 ft walls needs about 2 gallons for two coats.

Buy too little and you’re back at the store mid-project chasing a matching batch; buy too much and you’ve paid for a gallon that dries out in the garage. Here is how to get it right.

The formula

gallons = (wall area − openings) ÷ 350 × coats

A gallon of interior paint covers about 350 ft² per coat on primed, smooth walls — the spread rate printed on most manufacturer product data sheets. Textured or unprimed walls soak up more, so they cover less. When you buy, choose a low-VOC formula; the U.S. EPA explains why it matters for indoor air quality.

Worked example: a 12 × 12 ft room

With 8 ft ceilings, one door, and two windows:

1. Perimeter: (12 + 12) × 2 = 48 ft
2. Wall area: 48 × 8 = 384 ft²
3. Subtract openings: one door (21 ft²) + two windows (30 ft²) = 51 ft² → 333 ft²
4. Two coats: 333 × 2 = 666 ft²
5. Gallons: 666 ÷ 350 = 1.9 → 2 gallons

Coverage cheat sheet

Common mistakes

• Forgetting the second coat. Almost every color change needs two coats for even coverage. Always calculate for the coats you’ll actually apply.
• Not accounting for primer. Bare drywall or a big color change needs primer, which is a separate gallon count.
• Over-subtracting openings. Only subtract doors and large windows. Skipping this step is safer than over-counting — a little extra paint beats running out.

Related

Papering an accent wall instead? The wallpaper calculator handles rolls and pattern repeat. Patching drywall first? Size sheets and mud with the drywall calculator. When you’re ready, the full paint calculator covers whole-house exterior jobs too.