How Much Paint for a 12×12 Room?
A 12×12-ft room with 8-ft ceilings needs 3 gallons of paint for two coats on the walls, or 4 gallons for two coats on the walls and the ceiling. That assumes one standard door, two windows, and a typical 350 sq ft per gallon latex paint. If you are painting a 12-by-12 bedroom that already has a painted ceiling you like, buy the 3 gallons and spend the difference on better paint.
The math, step by step
This is exactly what our calculator runs, so you can check every number:
- Gross wall area: 2 × (12 + 12) × 8 = 384 sq ft.
- Subtract openings: one door at 20 sq ft and two windows at 15 sq ft each = 50 sq ft. That leaves 334 sq ft of wall.
- Ceiling: 12 × 12 = 144 sq ft. Total paintable with ceiling: 478 sq ft.
- Waste factor: add 10% for roller loading, tray leftovers, and touch-ups → 525.8 sq ft.
- Per coat: 525.8 ÷ 350 = 1.50 gallons for one coat.
- Two coats: 1.50 × 2 = 3.00 gallons, and because you cannot buy a fractional can, that rounds to 4 gallons.
That last rounding step surprises people. At 3.004 gallons you are a hair over three cans, and paint stores do not sell the remainder. Walls only is friendlier: 367.4 sq ft with waste ÷ 350 = 1.05 gallons per coat, 2.10 for two coats, so 3 gallons covers it with real margin left for touch-ups.
Nearby scenarios for a 12×12 room
| Scenario | Paintable area | With 10% waste | Buy |
|---|---|---|---|
| Walls only, 1 coat, 8-ft ceiling | 334 sq ft | 367 sq ft | 2 gallons |
| Walls only, 2 coats, 8-ft ceiling | 334 sq ft | 367 sq ft | 3 gallons |
| Walls + ceiling, 1 coat, 8-ft ceiling | 478 sq ft | 526 sq ft | 2 gallons |
| Walls + ceiling, 2 coats, 8-ft ceiling | 478 sq ft | 526 sq ft | 4 gallons |
| Walls only, 2 coats, 9-ft ceiling | 382 sq ft | 420 sq ft | 3 gallons |
| Walls + ceiling, 2 coats, 9-ft ceiling | 526 sq ft | 579 sq ft | 4 gallons |
| Walls + ceiling, 2 coats, 10-ft ceiling | 574 sq ft | 631 sq ft | 4 gallons |
| Walls + ceiling, 3 coats (deep color), 8-ft ceiling | 478 sq ft | 526 sq ft | 5 gallons |
Notice how forgiving the jump from 8-ft to 10-ft ceilings is once the ceiling is in the mix — the fourth gallon absorbs it. The expensive change is the third coat, which a saturated navy or charcoal will demand.
Twelve by twelve is the calculator's default room, so that link lands ready to go. Adjust for your exact room — a bumped ceiling height, a second door, or a bay window all move the total, and the result updates as you type.
Common questions
Does a 12×12 bedroom need primer?
Only in three cases: bare or patched drywall, a color change that goes lighter over a dark wall, or visible stains from water or smoke. Primer covers at roughly the same rate as paint, so a 12×12 room takes 2 gallons of primer for a single primer coat over the walls and ceiling. Tinting the primer toward your finish color often saves you a topcoat, which makes it close to free.
Can I get away with one coat in a 12×12 room?
Yes, if you are repainting the same color family in a premium paint over a smooth, previously painted surface. Two gallons will do walls and ceiling in one pass. Going one coat over a color change is where people regret it — patchiness shows up at the corners and under raking window light, and fixing it costs more than the gallon you saved.
Will I have paint left over from 4 gallons?
Roughly half a gallon, because the 10% waste factor is a cushion rather than a guarantee you will use it. That is deliberate. Keep the remainder in a sealed quart labeled with the room and the color code — bedroom walls pick up furniture scuffs, and a matching touch-up beats a re-roll of the whole wall two years from now.
Related
- How much paint for a 10×10 room — the small-bedroom and office numbers.
- How much paint for an average bedroom — the full 10×10 to 14×16 range.
- Paint cost per gallon in 2026 — turn 3 or 4 gallons into a dollar figure.
- Trim paint calculator — baseboards and casings are quarts of semi-gloss, counted separately.
- Paint calculator — any room size, any ceiling height.