Most rooms need 2 to 3 gallons of paint for two coats on the walls. A typical 12 × 14 ft bedroom with 9 ft ceilings takes about 3 gallons; a small 10 × 10 ft room takes 2.
The arithmetic: wall area minus doors and windows, times the number of coats, divided by 350 sq ft per gallon, then round up.
Common room sizes
Figures below assume one standard door (21 sq ft), two average windows (15 sq ft each), two coats, and 350 sq ft of coverage per gallon.
| Room | Ceiling | Wall area | Paintable | Gallons (2 coats) |
|---|---|---|---|---|
| 10 × 10 ft | 8 ft | 320 sq ft | 284 sq ft | 2 |
| 12 × 12 ft | 8 ft | 384 sq ft | 348 sq ft | 2 |
| 12 × 14 ft | 9 ft | 468 sq ft | 417 sq ft | 3 |
| 14 × 16 ft | 9 ft | 540 sq ft | 489 sq ft | 3 |
| 16 × 20 ft | 10 ft | 720 sq ft | 654 sq ft | 4 |
| 20 × 20 ft | 9 ft | 720 sq ft | 684 sq ft | 4 |
The formula
The clearest way to see it is to imagine the four walls unfolded flat into a single strip. Painting a room is painting that strip. Its length is the room's perimeter, its height is the ceiling height.
Four steps, and the only one people get wrong is the first.
- Perimeter × ceiling height. Add all four wall lengths, multiply by height. For a 12 × 14 room: (12+14) × 2 = 52 ft perimeter, × 9 ft = 468 sq ft.
- Subtract openings, about 21 sq ft per door, 15 sq ft per window. One door and two windows: 468 − 51 = 417 sq ft.
- Multiply by coats, almost always two. 417 × 2 = 834 sq ft of coverage needed.
- Divide by 350. That gives 834 ÷ 350 = 2.4 gallons. Round up to 3.
The common mistake is using floorarea instead of wall area. Floor area tells you nothing directly. A long narrow room and a square room with the same floor area have very different wall areas, and it's walls you're painting.
Whole houses
For a full interior, a reasonable planning figure is that wall area runs roughly 2.5 to 3 times the floor area. A 2,000 sq ft house therefore has somewhere around 5,000 to 6,000 sq ft of wall, or 12 to 16 gallons at two coats.
Budget separately for the parts people forget:
- Ceilings, roughly one gallon per 350 sq ft of floor area per coat. Usually flat white, usually a different product.
- Trim, doors and frames. Budget 2 to 4 gallons for a typical house. Different sheen, bought separately.
- Primer. A full extra coat's worth wherever you're covering bare drywall, patches, or a dramatic color change.
When to buy more than the math says
Add roughly 10 to 20% if any of these apply: textured walls, unprimed or patched drywall, a big color change (especially over dark reds or yellows), or spray application. Those are the situations where people run out mid-job.
Not sure how far a gallon goes? See how much a gallon of paint covers. Painting something large enough to consider a bucket? See how much 5 gallons covers.
Skip the arithmetic
Enter your own dimensions and get the exact figure instead of working from averages.
Open the Paint CalculatorFrequently asked questions
A 12x12 ft room with 8 ft ceilings has about 384 sq ft of gross wall area. After subtracting a door and a window, roughly 348 sq ft is paintable, about 2 gallons at two coats. Buy 2 and you'll have very little spare, so 3 is safer if the color change is significant.
For interior walls, a 2,000 sq ft house typically needs 12 to 16 gallons at two coats, plus 3 to 4 gallons for ceilings and 2 to 3 for trim. Floor area is a rough proxy at best. Wall area is what determines paint quantity, and layouts with more internal walls need more.
A 20x20 garage with 9 ft walls has about 720 sq ft of wall area. Bare or unprimed masonry and drywall are common in garages and drink far more paint, so plan on 4 to 5 gallons at two coats even though the arithmetic alone says 4.
Round up to the next whole gallon, and keep the leftovers. Touch-ups are inevitable, and paint mixed later from the same formula can still differ subtly in shade. A sealed, labeled part-gallon in the garage is worth more than the few dollars you'd save buying exactly enough.
More guides
How Much Does a Gallon of Paint Cover?
One gallon covers 350 to 400 sq ft in a single coat, though your walls will probably do worse.
How Much Does 5 Gallons of Paint Cover?
A bucket covers about 1,750 sq ft in one coat. Whether that saves you money depends on the job.
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