How much paint do I need for a room?

The short answer

A gallon of interior paint typically covers 350 to 400 sq ft of smooth wall per coat. A 12 × 12 ft room with 8 ft walls, one door and two windows has about 334 sq ft of paintable wall. Two coats with 10% extra for touch-ups comes to 2.10 gallons, so buy 2 gallons and 1 quart.

Step 1: Measure the walls

Measure the length and width of the room along the floor and the height from floor to ceiling, all in feet. Add up the four wall lengths and multiply by the height. You do not have to measure each wall on its own unless the room is not a simple rectangle.

For a 12 × 12 ft room with 8 ft walls, the four walls add up to 48 ft, and 48 × 8 = 384 sq ft. For an L-shaped room, measure each wall (length × height) and add them together.

Step 2: Subtract doors and windows

You will not paint the doors or the glass, so take their area off the wall total. Our calculators subtract 20 sq ft for each door and 15 sq ft for each window, which fits standard sizes. If you have a sliding door, a picture window or an archway, measure it instead of guessing.

1. Wall area: 384 sq ft.
2. One door and two windows: 20 + 15 + 15 = 50 sq ft.
3. Paintable area: 384 − 50 = 334 sq ft.

There is no need to subtract baseboards, outlets or small trim. The little bit of extra paint is your margin for touch-ups.

Step 3: Coverage and coats

Sherwin-Williams says a gallon of paint typically covers about 350 to 400 sq ft, and a gallon of primer about 200 to 300 sq ft. The exact figure for your paint is printed on the can or the product data sheet, so use that when you have it.

Textured walls and bare, unprimed drywall soak up more paint, so the paint calculator has presets of 300 and 250 sq ft per gallon for those surfaces.

Plan on two coats for most repaints. Angi lists unfinished drywall or plaster, wallpaper and covering a dark color with a light one as the usual reasons to prime first, and priming adds a coat of work.

Worked example: a 12 × 12 ft bedroom

1. Paintable wall area: 334 sq ft.
2. Two coats: 334 × 2 = 668 sq ft to cover.
3. At 350 sq ft per gallon: 668 ÷ 350 = 1.91 gallons.
4. Add 10% for touch-ups: 1.91 × 1.10 = 2.10 gallons.
5. Buy 2 gallons and 1 quart.

Do not forget the ceiling

Ceilings are usually painted with a flat ceiling paint, so count them separately from the walls. The ceiling area is simply length × width. A 12 × 12 ft ceiling is 144 sq ft; two coats with 10% extra comes to 0.91 gallons, so one gallon covers it.

Buying gallons, quarts and spares

• Round up to whole cans. A quart can cover a small remainder without buying a whole second gallon.
• Buy all the paint for a room at the same time. Tinted paint often cannot be returned, so a slightly generous estimate beats a second trip.
• If you need more than one gallon of a custom color, mix the cans together in a bucket before you start so small differences between batches even out.
• Keep a labeled leftover for touch-ups.

Common mistakes

• Using the floor area instead of the wall area.
• Forgetting the second coat.
• Using the coverage on the can for a textured or unprimed wall.
• Buying exactly the calculated amount with nothing extra for touch-ups.

Calculators for this job

These calculators do the arithmetic from this guide. Each card shows the result for a typical project; open one to enter your own measurements.

Frequently asked questions

Sources

1. Sherwin-Williams, How to Use Paint Calculator
2. Angi, How Many Coats of Primer Do I Need?
3. Painter's Solutions, Understanding Paint Coverage: How Much Do You Need?