A gallon of wall paint covers about 350 sq ft per coat, so a 12 × 12 ft room with 8 ft ceilings needs about 2.1 gallons for two coats on the walls — buy 2 gallons plus a quart, or 3 gallons. A 10 × 10 room needs 2 gallons. Run your own room in the QtyLab paint calculator (prefilled for 12 × 12); it gives gallons and quarts.
The paint formula, worked for a 12 × 12 room
- Wall area = 2 × (12 + 12) × 8 ft = 384 sq ft
- Subtract openings = 1 door (20 sq ft) + 2 windows (15 sq ft each) = 50 sq ft → 334 sq ft
- Two coats = 334 × 2 = 668 sq ft
- Add 10% for touch-ups, rough spots and what stays in the tray = 734.8 sq ft
- Gallons = 734.8 ÷ 350 = 2.1 gallons → 2 gallons + 1 quart (9 quarts), or 3 gallons
Coverage on the can is per coat. Most interior wall paints list somewhere around 250–400 sq ft per gallon; QtyLab uses 350 as the default. If your can says less — common with thick one-coat paints or rough, porous walls — put the label number in the calculator.
Paint for common room sizes (walls only)
8 ft ceilings, 1 door, 2 windows, 2 coats, 350 sq ft per gallon, 10% extra. Each row opens the calculator with those numbers.
| Room | Paintable walls | Exact gallons | Buy |
|---|---|---|---|
| 10 × 10 | 270 sq ft | 1.7 | 2 gal |
| 10 × 12 | 302 sq ft | 1.9 | 2 gal |
| 12 × 12 | 334 sq ft | 2.1 | 2 gal + 1 qt |
| 12 × 12, 9 ft ceiling | 382 sq ft | 2.4 | 2 gal + 2 qt, or 3 gal |
| 12 × 14 | 366 sq ft | 2.3 | 2 gal + 2 qt, or 3 gal |
| 14 × 16 | 430 sq ft | 2.7 | 3 gal |
| 12 × 20 | 462 sq ft | 2.9 | 3 gal |
Ceiling too? It’s length × width — 144 sq ft for a 12 × 12 room, which is about 0.9 gallon for two coats, so 1 gallon of ceiling paint.
Gallons by wall area
| Paintable area | Exact gallons (2 coats, +10%) | Buy |
|---|---|---|
| 200 sq ft | 1.26 | 1 gal + 2 qt, or 2 gal |
| 400 sq ft | 2.51 | 3 gal |
| 800 sq ft | 5.03 | 5 gal + 1 qt, or 6 gal |
| 1,200 sq ft | 7.54 | 8 gal |
One coat halves it: 400 sq ft at 1 coat is 1.26 gallons.
Quarts vs gallons
A quart is a quarter gallon — about 87 sq ft per coat at 350 sq ft per gallon. When the math lands just over a whole gallon, like the 2.1 gallons for a 12 × 12 room, a quart covers the gap. Quarts usually cost much more per ounce, so once you need 3 or more quarts, a full gallon is usually the better buy. Mix leftovers from different cans of the same color into one bucket (boxing) so the walls match.
When you need a third coat or primer
- Big color change (dark to light, or a deep red or yellow): plan on 3 coats, or a tinted primer plus 2.
- New drywall: prime first — fresh paper and mud soak up paint unevenly.
- Patched or stained walls: spot-prime the patches so they don’t show through.
- Same color, good condition: 1 coat may be enough; set coats to 1 in the calculator.
Mistakes that throw the count off
- Forgetting the second coat. Coverage on the can is per coat; two coats doubles the paint.
- Not subtracting doors and windows. On a small room that’s 50 sq ft per coat — more than a quart of paint over two coats.
- Using the label’s best case. Textured or porous walls cover less. Lean toward the low end of the label range.
- Buying walls and ceiling as one. Ceilings usually get a flat ceiling paint; count them separately.
- Running out mid-wall. Different batches can shift slightly in color. Buy enough up front and box the cans.
Shopping list for a 12 × 12 room (walls, 2 coats)
- 2 gallons + 1 quart of wall paint (or 3 gallons) — shop interior paint
- 1 roller frame, covers and tray — shop roller kits
- 1 angled sash brush (2½ in) for cutting in — shop angled brushes
- 1 roll of painter’s tape — shop painter’s tape
- 1 canvas drop cloth — shop drop cloths
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Hanging new drywall first? See how many sheets of drywall for a 12 × 12 room and the drywall calculator.
FAQ
How many gallons of paint do I need for a 12 × 12 room?
About 2.1 gallons for two coats on the walls with 8 ft ceilings, after subtracting 1 door and 2 windows and adding 10%. Buy 2 gallons plus a quart, or 3 gallons. The ceiling adds about 1 gallon.
How many square feet does a gallon of paint cover?
Most interior wall paints list about 250–400 sq ft per gallon per coat; 350 is a common planning number. Rough or porous walls cover less, so check the label on the can you buy.
Should I buy a quart or a gallon?
A quart is a quarter gallon, about 87 sq ft per coat at 350 sq ft per gallon. Use quarts to top up when you are just over a whole gallon; if you need 3 or more quarts, a full gallon is usually cheaper.
How much paint for a 10 × 10 room?
A 10 × 10 room with 8 ft ceilings, 1 door and 2 windows has about 270 sq ft of wall. Two coats with 10% extra is 1.7 gallons, so buy 2 gallons.
Do I need two coats of paint?
Usually yes for even color, especially over a different color or patched walls. Over the same color in good condition, one coat can be enough. Big color changes may need three coats or a tinted primer.
Coverage range (250–400 sq ft per gallon) from Behr Premium Plus Interior product data. All counts are from the QtyLab paint calculator (walls only; doors 20 sq ft, windows 15 sq ft). Coverage varies by product and surface — the number on your can wins. Estimates for planning only.
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