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How Much Paint Do I Need?
Direct answer: A 12 ft × 12 ft room with 8 ft ceilings needs about 2 gallons for one coat and 3 gallons for two coats of wall paint, at the standard coverage of 350 sq ft per gallon. Walls only — the ceiling needs about 1 extra gallon.
The formula
Wall area = 2 × (length + width) × ceiling height.
Gallons = wall area × coats ÷ 350.
Always round up to whole gallons — paint is sold by the gallon, and running out mid-wall leaves visible lines.
Worked example
A room has 400 sq ft of wall area and you want 2 coats at 350 sq ft per gallon:
400 ÷ 350 = 1.14 gallons per coat.
1.14 × 2 coats = 2.29 gallons, so you buy 3 gallons.
In cans: at 100 sq ft per can, 400 ÷ 100 = 4 cans per coat, so 8 cans for two coats. Try it with your own numbers in the Paint Coverage Calculator or the Paint Cans Calculator.
Gallons by room size
8 ft ceilings, smooth primed walls, 350 sq ft per gallon, walls only:
| Room | Wall area | 1 coat (buy) | 2 coats (buy) |
|---|---|---|---|
| 10 × 10 ft | 320 sq ft | 0.91 gal (1) | 1.83 gal (2) |
| 12 × 12 ft | 384 sq ft | 1.10 gal (2) | 2.19 gal (3) |
| 15 × 12 ft | 432 sq ft | 1.23 gal (2) | 2.47 gal (3) |
Subtract doors and windows you will not paint: a standard door is about 21 sq ft, a standard window about 15 sq ft.
Ceilings and primer
Ceiling area is length × width. A 12 × 12 ceiling is 144 sq ft, which is 0.41 gallons per coat — one gallon covers one coat.
Primer is a separate coat, bought separately. It usually covers less than finish paint (typically 200–300 sq ft per gallon), so check the label on the can you buy.
Try the calculators
Enter your exact room size instead of guessing from the table:
Paint Coverage Calculator Paint Cans CalculatorFrequently asked questions
How many gallons of paint do I need for a 12x12 room?
A 12x12 room with 8 ft ceilings has 384 sq ft of wall area. At 350 sq ft per gallon, that is about 2 gallons for one coat and 3 gallons for two coats.
How much paint do I need for one wall?
A 12 ft by 8 ft wall is 96 sq ft. At 350 sq ft per gallon, that is 0.27 gallons, so one quart covers it and one gallon is more than enough.
Does paint coverage include primer?
No. Primer is a separate coat and is bought separately. Primer usually covers less than finish paint, typically 200 to 300 sq ft per gallon, so check the label.
How many coats of paint do I need?
Two coats is the standard for an even, durable finish, especially for a colour change or new drywall. One coat may be enough when repainting the same colour.
How much paint do I need for the ceiling?
Ceiling area is length times width. A 12x12 ceiling is 144 sq ft, which is 0.41 gallons per coat at 350 sq ft per gallon, so one gallon covers one coat.
How we check our calculators: every calculator shows its formula with a worked example. Read how our calculators are checked.