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Paint calculator: how much paint do I need?
One gallon covers about 350 to 400 sq ft per coat (Sherwin-Williams), so a 12 × 12 ft room with 8 ft ceilings needs about 2 gallons for two coats on the walls.
How much paint for a room: chart
Two coats on the walls of a room with 8 ft ceilings, one door and two windows, at 350 sq ft per gallon per coat.
| Room | Wall area (sq ft) | Gallons | Buy |
|---|---|---|---|
| 10 × 10 ft | 269 | 1.5 | 2 gal |
| 10 × 12 ft | 301 | 1.7 | 2 gal |
| 12 × 12 ft | 333 | 1.9 | 2 gal |
| 12 × 14 ft | 365 | 2.1 | 2 gal + 1 qt |
| 14 × 16 ft | 429 | 2.5 | 2 gal + 2 qt |
| 16 × 20 ft | 525 | 3 | 3 gal |
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Wallpaper rolls by room size
| Room | Wall area (sq ft) | Rolls (56 sq ft, 15% waste) |
|---|---|---|
| 10 × 10 ft | 269 | 6 |
| 10 × 12 ft | 301 | 7 |
| 12 × 12 ft | 333 | 7 |
| 12 × 14 ft | 365 | 8 |
| 14 × 16 ft | 429 | 10 |
How the paint calculator works
Wall area = perimeter × ceiling height, minus about 21 sq ft per door and 15 sq ft per window. Gallons = area × coats ÷ coverage. Sherwin-Williams puts a gallon at about 350–400 sq ft per coat; we default to 350, the low end, so you don’t run short. We round up to the nearest quart, and to a whole gallon when you’d need three quarts.
Wallpaper: wall area ÷ (roll area less a pattern-matching allowance). A US double roll of 20.5 in × 33 ft covers about 56 sq ft; check the label, as roll sizes vary.
Questions
How much paint do I need for a 12 × 12 room?
About 1.9 gallons for two coats on the walls of a 12 × 12 ft room with 8 ft ceilings, one door and two windows: buy 2 gallons.
How many square feet does a gallon of paint cover?
About 350 to 400 square feet per coat on smooth, primed walls, according to Sherwin-Williams. Rough or porous surfaces take more.
Do I need two coats of paint?
Usually, yes: two coats give even color and wear better. A big color change or fresh drywall may need primer plus two coats.
How much paint for a ceiling?
A 12 × 12 ft ceiling is 144 sq ft: about 0.8 gallons for two coats. Tick “Include the ceiling” in the calculator.
Should I buy a little extra paint?
Yes: keep a quart for touch-ups, and buy all you need at once so the tint matches.
How many rolls of wallpaper do I need?
About 7 double rolls for a 12 × 12 ft room with 8 ft ceilings, allowing 15% for pattern matching.
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