Paint Calculator

The short answer

Measure around the room and multiply by the wall height, take off about 21 sq ft for each door and 15 sq ft for each window, then multiply by the coats and divide by the coverage on the can. With no number from the can, use 350 sq ft per gallon.

A 12 × 15 ft bedroom with 8 ft ceilings, one door and two windows has 381 sq ft of wall. Two coats take 2.18 gallons, so buy 2 gallons and 1 quart.

How to measure

1. The room: measure it wall to wall both ways, along the floor. For one wall, such as an accent wall, measure it corner to corner.
2. The height: measure from the floor to the ceiling.
3. The doors and windows: count them. Each door takes off about 21 sq ft (a 3 × 7 ft door) and each window 15 sq ft (a 3 × 5 ft window).
4. The can: look for the coverage on the label, in square feet per gallon. It’s the best guide for that paint.

How to use the calculator

1. Choose a whole room or one wall.
2. Enter the size and the height, then the number of doors and windows. A room you entered in another tool carries over.
3. Choose the coats and the surface, and enter the coverage from your can if you have it.
4. Add the ceiling or a coat of primer if you need them, and read the result: the gallons and quarts to buy, a shopping list with the exact amounts and a picture of the walls.
5. Save or share it. Copy link keeps your numbers in the address.

How we calculate

The amounts are estimates. If your can gives its own coverage, that number comes first.

• The walls: the distance around the room, or one wall’s width, times the wall height. Each door takes off 21 sq ft and each window 15 sq ft.
• Coverage: a gallon covers about 350 to 400 sq ft per coat, and more on a smooth, primed surface. The figure on a can leaves out what a rough or porous wall and the roller soak up, so the calculator uses the low end, 350 sq ft. That builds in a margin for waste.
• Coats: two on the walls, and one on the ceiling unless you change it.
• The surface: a lightly textured wall takes about 20% more paint, and a heavy texture or a popcorn ceiling about 2 times as much.
• The ceiling: the room’s length times its width, with the same coverage and surface as the walls.
• Primer: one coat over the walls, and the ceiling if it’s painted too, at 300 sq ft per gallon, the top of what a gallon of primer covers.
• What to buy: the exact gallons rounded up to whole quarts, four to a gallon. When more than half a gallon would be quarts, it’s a gallon instead.

Worked examples

Worked example

A 12 × 15 ft bedroom with 8 ft ceilings

What we know

• Room: 12 ft × 15 ft, 8 ft ceilings
• Openings: one door and two windows
• Paint: 2 coats on the walls

How it works out

1. Walls: 432 sq ft less 51 sq ft for the openings = 381 sq ft.
2. Wall paint: 381 sq ft × 2 ÷ 350 = 2.18 gal, so 2 gallons and 1 quart.

2 gallons and 1 quart of wall paint.

Worked example

A 16 × 20 ft living room, walls and ceiling

What we know

• Room: 16 ft × 20 ft, 9 ft ceilings
• Openings: two doors and four windows
• Paint: 2 coats on the walls, 1 coat on the ceiling

How it works out

1. Walls: 648 sq ft less 102 sq ft for the openings = 546 sq ft.
2. Wall paint: 546 sq ft × 2 ÷ 350 = 3.12 gal, so 3 gallons and 1 quart.
3. Ceiling paint: 320 sq ft × 1 ÷ 350 = 0.91 gal, so 1 gallon.

3 gallons and 1 quart of wall paint, 1 gallon of ceiling paint.

Worked example

A 12 ft accent wall in a dark color, with primer

What we know

• One wall: 12 ft wide, 8 ft high, no doors or windows
• Paint: 2 coats on the walls, a coat of primer

How it works out

1. Wall: 96 sq ft.
2. Wall paint: 96 sq ft × 2 ÷ 350 = 0.55 gal, so 1 gallon.
3. Primer: 96 sq ft ÷ 300 = 0.32 gal, so 2 quarts.

1 gallon of wall paint and 2 quarts of primer.

How much paint for a room: chart

Wall paint for common room sizes with 8 ft ceilings, one door and two windows, two coats at 350 sq ft per gallon.

How much paint for a ceiling

The ceiling of each of the same rooms, at 350 sq ft per gallon.

A popcorn or heavily textured ceiling takes about 2 times as much. In a house built before 1977, have a textured ceiling tested for asbestos before you paint it.

Primer and coats

• When to prime: walls that are already painted and in good shape usually need no primer. Prime new drywall, patches, stains and glossy paint, and prime for a big change of color, with the primer tinted toward the new color.
• Bare drywall: it can take two coats of primer, or a self-priming paint in two coats.
• One coat or two: one can be enough for the same or a similar color, or over a tinted primer. Count on two otherwise.
• Between coats: wait the recoat time on the can, often 1 to 4 hours for water-based interior paint.

Buying the paint

• Gallons and quarts: paint comes in quarts, gallons and 5-gallon pails. A quart covers about 100 sq ft.
• Mix the cans: with more than one can, pour them all into a big bucket and mix them before you start, so the color is the same on every wall.
• Trim, doors and cabinets: they take their own paint, often 1 to 2 quarts. The calculator counts only the walls, the ceiling and primer.
• Keep the leftovers: round up and keep what’s left for touch-ups.
• Wallpaper instead? Paper is counted by the strip, not by the gallon: use the wallpaper calculator.

Painting safely

• Lead paint: homes built before 1978 may have lead-based paint, and renovation and painting work on it can make lead dust. In an older home, follow the EPA’s lead-safe work practices.
• Fresh air: open windows while you paint and follow the ventilation advice on the label.

Painting a nursery? The nursery checklist generator lists what else the room needs before the baby comes.

Then choose the art for the freshly painted wall with the wall art size calculator, or pick the colors first with the room color palette generator. New blinds for the windows? The blind size calculator gives the size to order.