Room Paint Calculator
Buying paint by guesswork usually ends one of two ways: a second trip to the store mid-project, or a shelf of leftover gallons you will never open again. Neither is fun.
This calculator does the wall math properly — subtracting standard door and window areas, adding coats, and optionally including the ceiling — then converts the result into gallons and an estimated cost at three quality tiers.
| Measure | Value |
|---|---|
| Wall area (after 1 door, 1 window) | 348 sq ft |
| Total paintable area × 2 coats | 696 sq ft |
| Paint needed (mid) | 2 gal · $90 |
How this tool works
- Wall area is the room perimeter times wall height, minus about 21 sq ft per door and 15 sq ft per window.
- Coverage is assumed at 350 sq ft per gallon per coat — the industry standard for smooth, previously painted walls.
- Rough, porous, or dramatically color-changing surfaces need more paint; add a coat rather than trusting one heavy pass.
- Cost tiers reflect typical retail pricing for budget, mid-range, and premium interior paint.
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12×12 room with 8-foot ceilings has roughly 384 sq ft of wall area before subtracting openings. With one door and one window, two coats of paint takes about 2 gallons for the walls, plus another gallon if you are painting the ceiling.
How many square feet does a gallon of paint cover?
Most interior paints cover 350–400 sq ft per gallon on smooth, sealed surfaces. Textured walls, bare drywall, and strong color changes reduce effective coverage significantly, sometimes to 250 sq ft per gallon.
Do I really need two coats of paint?
Almost always, yes. One coat rarely delivers uniform color and sheen, even with paint-and-primer products. The exceptions are repainting with the identical color or using very high-end paint over a well-prepped, similar-toned wall.
Is expensive paint worth it?
Premium paint carries more pigment and resin, which means better coverage in fewer coats, easier cleaning, and longer life before it looks tired. For high-traffic rooms, the math usually favors the better can — you buy less of it and repaint less often.