How many gallons of paint do I need for a 12x12 room?

For an average 12-by-12 room with 8-foot ceilings, you need roughly 1.5 gallons for two coats of the walls — so buy 2 gallons. The four walls total about 384 square feet of wall area before subtracting a door and window, and at 350 to 400 square feet per gallon per coat, one gallon covers a single coat with a little to spare. Since almost every job needs two coats for even color, plan on two gallons and keep the leftover for touch-ups. Add another quart or gallon if you are also painting the ceiling.

Does a gallon of paint really cover 400 square feet?

On a smooth, sealed, previously painted wall of a similar color, yes — 350 to 400 square feet per coat is realistic. But that figure is a best case. Bare drywall, fresh joint compound, textured or porous surfaces, and dramatic color changes all drink more paint and can drop real coverage to 250 to 300 square feet per gallon. The number on the can is measured under ideal conditions; treat 350 as a safe planning figure for normal walls and expect less on anything rough, new or unpainted.

How do you calculate how much paint you need?

Measure the perimeter of the room, multiply by the ceiling height to get total wall area, subtract about 20 square feet for each door and 15 for each window, then divide by 350 for one coat. Multiply by the number of coats — usually two. For example, a room with a 48-foot perimeter and 8-foot walls is 384 square feet; minus a door and window it is around 350, so one gallon per coat, two gallons for the job. Round up and keep a little in reserve; running out mid-wall risks a visible lap mark.

Why does dark or bright paint need more coats?

Because deep and vivid colors use less white pigment and more transparent tint, so they hide the surface beneath less well and need extra coats — sometimes three — for even, opaque color. Reds, deep blues and bright yellows are the usual culprits. The fix that saves paint and time is a tinted primer: having the store tint a gray or colored primer toward your final color gives the topcoat a head start, so you reach full coverage in fewer finish coats. Two coats over a tinted primer usually beats three coats over white.

Should you always apply two coats of paint?

For a lasting, even finish, almost always yes. A single coat can look patchy, show roller lines and reveal the old color underneath, especially with lighter or cheaper paints, and it wears through sooner. Two coats give uniform color, better durability and a proper film thickness. The exceptions are a same-color refresh over a sound existing coat, or certain premium one-coat paints on a similar color — and even those benefit from a second pass in high-traffic rooms. Budget paint quantity for two coats from the start.

How Many Square Feet Does a Gallon of Paint Cover?

Written & researched by Priya Anand DIY & Tools Editor

Updated October 2026

Wide view of a person rolling fresh paint onto an interior wall, in soft overcast light

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One gallon of interior paint covers about 350 to 400 square feet per coat on a smooth, sealed wall. That is roughly the wall area of an average 12-by-12 room in a single coat. Real coverage drops on surfaces that drink paint — bare drywall, fresh joint compound, textured or porous walls, and dramatic color changes can pull it down to 250 to 300 square feet a gallon. Because almost every job needs two coats for even color, plan your paint quantity for two coats, not one, and round up so you never run out mid-wall.

What changes the coverage?

The 350-to-400 figure on the can assumes ideal conditions. Five things pull real-world coverage below it.

Factor	Effect on coverage
Smooth, previously painted wall	Best case; full 350–400 sq ft
Bare drywall or fresh joint compound	Porous; drops to ~250–300 (prime first)
Textured or knockdown walls	More surface area; noticeably less
Dark-to-light or bold color change	Needs extra coats for opacity
Thin / cheap paint	Less pigment; poorer hide per coat

Priming bare or patched surfaces first is what protects your coverage — an unprimed wall soaks up the first coat unevenly and wastes paint, which is one more reason new drywall and repairs get a primer before the color goes on.

Three-quarter view of a person rolling fresh paint onto an interior wall, in warm evening lamplight

How do I estimate gallons for a room?

The math is quick and worth doing before you buy.

Perimeter × height. Add up the lengths of all walls and multiply by ceiling height. A room 12×12 with 8-foot walls: perimeter 48 ft × 8 ft = 384 sq ft.
Subtract openings. Take off about 20 sq ft per door and 15 per window. One door and one window: roughly 350 sq ft left.
Divide by 350 for one coat: about one gallon.
Multiply by coats. Two coats: two gallons.

Add a quart or gallon if you are painting the ceiling, and always round up. Running short in the middle of a wall means either a rushed store trip or a visible lap line where a fresh batch meets a dried edge. A little leftover paint is also the easiest way to touch up scuffs later.

Wide view of a person rolling fresh paint onto an interior wall, in warm late-afternoon light

Why plan for two coats?

Because one coat rarely looks finished. A single pass tends to show roller streaks, patchy sheen and the old color ghosting through, and it builds too thin a film to wear well. Two coats deliver even color, a consistent sheen and the durability the paint is rated for. Deep and vivid colors — reds, bold blues, bright yellows — hide even less and sometimes want a third coat, which is where a tinted primer earns its keep: tint the primer toward your final color and the topcoats reach full opacity in fewer passes. The relationship between coats and dry time matters too — give each coat its full recoat window, covered in how long to wait between coats.

Over-the-shoulder view of a person rolling fresh paint onto an interior wall, in soft early-morning light

How much paint should I actually buy?

For a standard bedroom, two gallons of wall paint covers two coats with a touch-up reserve. For a large living room or an open-plan space, measure and calculate rather than guessing — the perimeter method above takes two minutes and saves both an overbuy and a mid-job shortfall. Buy all the paint for one room in a single purchase and, ideally, have the store box (intermix) multiple gallons together, so there is no batch-to-batch color shift across a big wall. The paint grade affects hide per coat, so a premium paint can genuinely cover in fewer coats — the trade-offs are in best interior paint, and the right roller lays it more evenly, in best paint rollers.

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