How Much Paint for a 12x12 Room?

Updated 2026-07-19

The 12×12 bedroom is the most common room in American housing — kids rooms, guest rooms, home offices, rentals. The paint math is mercifully simple, and once you have done it for this room you can scale the same four steps to the whole house.

The short answer is 2 gallons for the walls. The longer answer below shows where that number comes from, plus what to buy for the ceiling and trim so you are not making a second trip.

Step 1: Wall area = perimeter × height

A 12×12 room has a perimeter of 48 feet (12 + 12 + 12 + 12). With standard 8-foot ceilings, that is 48 × 8 = 384 square feet of wall area.

Nine-foot ceilings change the number fast: 48 × 9 = 432 square feet, a 12.5% jump. Vaulted or sloped ceilings — measure each wall separately, tallest and shortest points, and average them.

Step 2: Subtract the openings

You do not paint doors and windows, so do not buy paint for them. The standard deductions pros use are 21 square feet per door and 15 per average window. A typical 12×12 bedroom has one door and two windows: subtract 21 + 30 = 51 square feet, leaving 333 square feet of paintable wall.

If the room has something bigger — a wide cased opening to a bathroom, mirrored closet doors you are leaving alone — measure the actual opening and subtract the real number instead.

Step 3: Coats and coverage

Plan on two coats for any color change, and use 375 square feet per gallon as your planning number — quality interior paint covers 350 to 400 on smooth, previously painted drywall. The math: 333 × 2 coats = 666 square feet of coverage needed, divided by 375 is 1.78 gallons.

Verdict: buy 2 gallons. You will use about a gallon and three-quarters, and the leftover becomes your touch-up stash for the next decade of furniture dings. Repainting the same color over walls in good shape? One careful coat might do it, but 2 gallons is still the safer buy — batch-matched touch-up paint is worth more than the $40 you would save.

Do not forget the ceiling and trim

The ceiling is a separate product — flat ceiling paint, usually one coat. A 12×12 ceiling is 144 square feet, which takes under half a gallon, so a single gallon leaves you plenty for the hallway next weekend.

Trim is its own line item too. A 12×12 room runs about 60 to 80 linear feet of baseboard plus door and window casing, and one quart of semi-gloss handles two coats on all of it with a little to spare.

One more spot people forget: the closet interior. Painting the inside of a standard reach-in closet adds roughly 40 to 50 square feet — one coat is fine in there — so figure another quart into the wall paint. And if the door itself is getting painted, a standard interior door is about 20 square feet per side, so two coats on both faces eats most of a quart of trim paint on its own.

Adjust for the real world

If your room is not exactly 12×12 — and most are not — enter your real wall lengths, ceiling height, and openings into the paint calculator and it will hand you the gallon count for your exact room, ceiling and trim included.

1. Heavy texture (orange peel, knockdown): drop coverage to 250–300 sq ft per gallon and budget 2.5 to 3 gallons.
2. New unpainted drywall: add a gallon of drywall primer — the first coat of paint soaks in and covers poorly without it.
3. Dark to light color change: a tinted primer plus two coats beats three coats of paint every time.
4. One accent wall (8 × 12 = 96 sq ft): plan on about half a gallon for two coats — deep base colors often need a third pass, so buy the gallon.