How much paint do I need to paint a room?
A standard 12 × 12 ft room usually needs about 2 gallons of paint for two coats. The exact amount depends on your wall area, how many coats you're applying, and how much space your doors and windows take up. Here's how to work it out for any room — and how to turn the answer into a smart shopping list.
The simple formula
Every paint estimate comes down to one calculation:
Gallons = (wall area − openings) × coats ÷ 350
- Wall area = 2 × (length + width) × ceiling height
- Openings = about 21 sq ft per door and 15 sq ft per window
- 350 = the square feet one gallon covers in a single coat
Then round up to the next full gallon. That's it.
A worked example
Say you're painting a 12 × 12 ft room with 8 ft ceilings, one door, two windows, and two coats:
- Wall area: 2 × (12 + 12) × 8 = 384 sq ft
- Subtract openings: 384 − 21 − (2 × 15) = 333 sq ft
- Two coats: 333 × 2 = 666 sq ft of painting
- Divide by 350: 666 ÷ 350 = 1.9 → 2 gallons
Skip the math
Enter your room size, coats, doors, and windows into our free paint calculator and get the exact number of gallons — plus the cost — instantly.
Open the Paint CalculatorHow many coats do you need?
| Situation | Coats |
|---|---|
| Repainting a similar color | 1–2 |
| New color, similar depth | 2 |
| Light over dark (or dark over light) | 2–3 + primer |
| New or patched drywall | Primer + 2 |
What changes the 350 sq ft rule
Coverage is the assumption that moves your total most, so adjust it honestly:
- Texture: orange-peel and knockdown walls drink paint — figure 300 sq ft per gallon; heavy texture, less.
- Porous surfaces: bare drywall, fresh patches, and flat-finish repaints absorb the first coat; primer restores normal coverage.
- Application method: rolling matches the label numbers; an airless sprayer uses 20–30% more to overspray and the hose. Brushes are slow but no thirstier than rollers.
- Color change: the math above counts coats — the real question is how many you'll need. Dramatic changes are a three-coat (or tinted-primer) job.
Don't skip primer when it matters
Primer seals porous surfaces and helps your color cover evenly. Use it on bare drywall, patched areas, water stains, and any dramatic color change. Treat primer as one extra coat in the formula above — and note it covers a little less per gallon (200–300 sq ft), so a full prime coat of an average room takes 1–2 gallons.
Quick reference by room size
For walls only, 8 ft ceilings, two coats (round up at the store):
| Room | Approx. paint (2 coats) |
|---|---|
| Small bedroom — 10 × 10 ft | ~2 gallons |
| Bedroom — 12 × 12 ft | ~2 gallons |
| Living room — 14 × 16 ft | ~3 gallons |
| Open living — 15 × 20 ft | ~3 gallons |
| Add a ceiling | +1 gallon per ~350 sq ft |
| Add trim (per room) | +1 quart of semi-gloss |
Painting several rooms? Run each through the formula and total the same colors together — and see what painting a whole house costs for per-room and whole-home budgets. Taller ceilings scale it up fast; the 12×12 room example works through 8, 9, and 10 ft walls.
Turn the estimate into a shopping list
- Buy all of one color at once so the tint batch matches; note the formula code from the label for future touch-ups.
- Quarts fill the gaps. A quart covers ~87 sq ft — when you're barely over a gallon, a gallon plus a quart beats paying for two gallons (if your color tints in quarts).
- Go 5-gallon when one color needs 4+. Whole-floor neutrals are 10–20% cheaper per gallon in a bucket, and it's one guaranteed batch.
- Test with a sample quart before committing a room to a color you've only seen on a card.
- Supplies: a roller and tray, an angled brush for cutting in, painter's tape, and a drop cloth — $25–$50 if you're starting from nothing.