Paint Calculator

Work out how many gallons of paint you need for your walls and ceiling.

Results

Paintable wall area: 366 ft²
Wall paint: 2.091 gal
Gallons to buy: 3 gal
Gallons plus quarts: 2 gal + 1 qt

Ceiling

Ceiling area: 168 ft²
Ceiling paint: 0.48 gal

Enter your room's size, the number of doors and windows, and how many coats you're planning. You'll see the paintable wall area and the gallons you need, and whether a gallon plus a quart or two will do, so you don't end up short or with years of leftovers.

How to use it

Measure the room's length and width along the floor, and the wall height from floor to ceiling.
Enter how many doors and windows there are. The defaults subtract 20 ft² per door and 15 ft² per window. Change them if yours are unusually large, like patio doors or picture windows.
Set the number of coats. Two is the default and is what most color changes need.
Check the coverage figure on your can. The tool uses 350 ft² per gallon, the conservative end of the 350 to 400 range many brands print.
Tick "include ceiling" if you're painting it too.

Tips for a better estimate

Rough, textured or unpainted surfaces like new drywall, stucco or bare wood soak up more paint. Lower the coverage number, or plan on a primer coat.
Going from a dark color to a light one, or the reverse, often takes an extra coat.
Trim, doors and cabinets are usually painted in a different sheen, so estimate them separately.
If two gallons comes out just over a round number, gallons plus quarts can save money. Compare prices, though, since quarts usually cost more per ounce.
Write the color code and brand on the lid of your leftover can for touch-ups.

How it works

Wall area is the room's perimeter times its height, minus doors and windows. Gallons are that area times the number of coats, divided by your can's coverage, rounded up to the next gallon or quart.

Walls = 2 × (length + width) × height − 20 ft² per door − 15 ft² per window.
Gallons = area × coats ÷ coverage (350 ft²/gal by default). Ceiling = length × width × coats ÷ coverage.

Worked examples

A 12 × 14 ft bedroom

With 8 ft walls, one door and two windows: 2 × (12 + 14) × 8 = 416 ft², minus 20 and 30 for openings, leaves 366 ft². Two coats at 350 ft²/gal is 2.091 gallons. Buy 3 gallons, or 2 gallons plus 1 quart. One coat on the 168 ft² ceiling needs another 0.48 gallons, so a separate gallon of ceiling paint covers it.

A 10 × 10 ft room

With 8 ft walls, one door and one window, using a paint rated at 400 ft²/gal: 285 ft² of wall × 2 coats = 1.425 gallons. That's 2 gallons, or 1 gallon plus 2 quarts.

A large 20 × 15 ft living room

With 9 ft ceilings, two doors and four windows, and a single coat of the same color: 530 ft² ÷ 350 = 1.514 gallons. Buy 2 gallons, or 1 gallon plus 3 quarts.

Paint needed by room size

Assumes 1 door, 2 windows, 2 coats on walls, 1 coat on the ceiling, 350 ft²/gal.

Wall and ceiling paint for common rooms
Room	Wall area	Wall paint	Ceiling paint
10 × 10 ft, 8 ft walls	270 ft²	1.54 gal (1 gal + 3 qt)	0.29 gal
10 × 12 ft, 8 ft walls	302 ft²	1.73 gal (1 gal + 3 qt)	0.34 gal
12 × 12 ft, 8 ft walls	334 ft²	1.91 gal (2 gal)	0.41 gal
12 × 14 ft, 8 ft walls	366 ft²	2.09 gal (2 gal + 1 qt)	0.48 gal
14 × 16 ft, 8 ft walls	430 ft²	2.46 gal (2 gal + 2 qt)	0.64 gal
16 × 20 ft, 9 ft walls	598 ft²	3.42 gal (3 gal + 2 qt)	0.91 gal

FAQ

How much paint do I need for a 12 × 12 room?

With 8 ft walls, one door, two windows and two coats, about 1.91 gallons, so 2 gallons. The ceiling adds about 0.41 gallons for one coat.

How many square feet does a gallon of paint cover?

Many brands list 350 to 400 ft² per gallon on the can. This calculator uses 350 by default, so it leans toward a little extra. Check your can and adjust it.

How do I calculate wall square footage for painting?

Add up the room's perimeter (2 × length + 2 × width), multiply by the wall height, and subtract about 20 ft² per door and 15 ft² per window.

How much paint do I need for a ceiling?

Multiply length by width and divide by coverage. A 12 × 14 ceiling is 168 ft², about 0.48 gallons per coat.

Do I need two coats of paint?

Usually, for an even finish, especially when changing colors. A fresh coat of the same color in good condition can sometimes get by with one.

Can I use this for exterior painting?

Yes, for a rough estimate. Treat each wall as a rectangle (and gable ends as triangles you add on). Exterior siding is often rougher than drywall, so lower the coverage number to match the paint can's guidance.