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.
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 |
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.
Quick reference by room size
For walls only, 8 ft ceilings, two coats (round up at the store):
| Room size | Approx. paint (2 coats) |
|---|---|
| 10 × 10 ft | ~2 gallons |
| 12 × 12 ft | ~2 gallons |
| 14 × 16 ft | ~3 gallons |
| Add a ceiling | +1 gallon per ~350 sq ft |
What else you'll need
Beyond the paint itself: a roller and tray, an angled brush for cutting in, painter's tape, and a drop cloth. Buy all your paint at once so the color batch stays consistent, and keep a little leftover for touch-ups.