Quick answer: Most interior paint covers 350–400 sq ft per gallon. A 12 × 12 ft room with 8 ft walls, one door and two windows has about 333 sq ft of wall, so two coats need about 1.9 gallons. Buy 2 gallons.
Paint is expensive, and running out partway through a wall can leave visible lap marks if the second can is from a different batch. Working out the quantity before you shop is quick.
Step 1: Measure the Wall Area
Wall area = 2 × (Length + Width) × Height
For a 12 × 12 ft room with 8 ft walls: 2 × (12 + 12) × 8 = 384 sq ft.
Step 2: Subtract Doors and Windows
A standard door is about 21 sq ft (3 × 7 ft) and an average window about 15 sq ft (3 × 5 ft). One door and two windows remove 51 sq ft, leaving 333 sq ft.
Step 3: Multiply by the Number of Coats
Two coats are standard, especially when changing color: 333 × 2 = 666 sq ft.
Step 4: Divide by Coverage
Gallons = Area × Coats ÷ Coverage
666 ÷ 350 = 1.9 gallons. In metric, use about 10 m² per litre: a room with 31 m² of wall needs about 6.2 litres for two coats.
Skip the math: enter your room size, openings and coats and get gallons, quarts or litres, plus which cans to buy. Open the free Paint Calculator →
Paint Needed by Room Size
Two coats at 350 sq ft per gallon, 8 ft walls, one door and two windows:
| Room size | Wall area | Walls (2 coats) | Ceiling (2 coats) |
|---|---|---|---|
| 10 × 10 ft | 269 sq ft | 1.5 gal | 0.6 gal |
| 12 × 12 ft | 333 sq ft | 1.9 gal | 0.8 gal |
| 12 × 14 ft | 365 sq ft | 2.1 gal | 1 gal |
| 14 × 16 ft | 429 sq ft | 2.5 gal | 1.3 gal |
| 16 × 20 ft | 525 sq ft | 3 gal | 1.8 gal |
| 20 × 20 ft | 589 sq ft | 3.4 gal | 2.3 gal |
What Affects Coverage?
- Surface: new drywall, bare plaster and textured walls absorb more paint. Prime them first.
- Color change: covering a dark color with a light one may need a primer and an extra coat.
- Paint quality: better paints usually hide in fewer coats.
- Application: rollers with a thick nap and sprayers use more paint than a standard roller.
Buying Tips
- If you need just over a gallon, buy a gallon and a quart instead of two gallons.
- For large rooms, a 5-gallon bucket is usually cheaper per gallon.
- Mix all cans of the same color in a bucket (boxing) for a consistent shade.
- Keep a little paint for touch-ups and label it with the room and color code.
Hanging new drywall first? Read how many sheets of drywall you need.
Frequently Asked Questions
How much paint do I need for a 10×10 room?
With 8 ft walls, one door and two windows, a 10 × 10 room has about 269 sq ft of wall, so two coats need about 1.5 gallons. Buy one gallon and two quarts, or two gallons.
How many square feet does a gallon of paint cover?
Typically 350–400 sq ft per coat on smooth, previously painted walls, and less on new or textured surfaces.
How many coats of paint do I need?
Two coats for most jobs. One coat may be enough when repainting the same color with a high-quality paint.
Related Guides
- How to Measure a Room for Flooring (Step-by-Step)
- How Many Tiles Do I Need for a Bathroom Floor or Shower?
- How Many Sheets of Drywall Do I Need for a Room?
Try the free Paint Calculator or browse all home improvement calculators.