How much paint do I need?
Find the wall area, subtract doors and windows, multiply by the number of coats, and divide by the coverage on the can. Most wall paint covers 350–400 sq ft per gallon on smooth, previously painted walls.
Gallons = (room perimeter × wall height − doors × 20 − windows × 15) × coats ÷ coverage
A 12 × 14 ft room with 8 ft walls has a perimeter of 52 ft, so 52 × 8 = 416 sq ft of wall. Take off one door (20 sq ft) and two windows (30 sq ft) and you have 366 sq ft. Two coats at 350 sq ft per gallon is 366 × 2 ÷ 350 = 2.1 gallons. At typical prices the cheapest way to buy that is 2 gallons and 1 quart.
Painting the ceiling too? It's 12 × 14 = 168 sq ft, so two coats take 0.96 gallons, or 1 gallon of ceiling paint.
Paint coverage and sizes
| Item | Typical figure |
|---|---|
| Wall paint, smooth surface | 350–400 sq ft per gallon |
| Rough, textured or bare surfaces | 250–300 sq ft per gallon |
| Primer | About 300 sq ft per gallon |
| Standard door | About 20 sq ft |
| Standard window | About 15 sq ft |
| Quart | Covers about 85–100 sq ft |
| 5-gallon bucket | Covers about 1,750–2,000 sq ft per coat |
Read the coverage on your can and enter it. The calculator buys the cheapest mix of 5-gallon buckets, gallons and quarts at the prices you set, so a 4.5 gallon job might come out as one bucket rather than five gallons.
Exterior paint calculator
For the outside of a house, enter the house's footprint as the room length and width and the wall height to the eaves. The calculator multiplies the perimeter by the height. Add each gable as a triangle with its base and height. Exterior siding is rougher than drywall, so start at 300 sq ft per gallon and use 250 for rough wood or stucco.
A 40 × 30 ft two-story house with 18 ft walls has 140 × 18 = 2,520 sq ft of wall. Take off 2 doors and 16 windows (280 sq ft) and add two gables at 30 ft wide by 7.5 ft tall (225 sq ft). That's 2,465 sq ft. Two coats at 300 sq ft per gallon is 16.4 gallons: three 5-gallon buckets and 2 gallons.
When to prime and how many coats
Two coats is the norm for a color change and gives even sheen. One coat can work when you repaint the same color. Prime new drywall, bare wood, patched areas, stains, and big changes from dark to light. Paint-and-primer products still usually need two coats over bare surfaces. Follow the label.
Interior painting estimate calculator
For an estimate, add every room, switch on ceilings, and enter trim as linear feet. Baseboard length is close to the room's perimeter. The calculator figures trim at about 4 in wide and buys it in quarts or gallons.
Labor is based on production: the square feet a painter rolls and cuts in per hour, per coat. The default is 150 sq ft per hour for interiors and 120 for exteriors, after prep. Set your own rate, since prep, ceilings and furniture moving vary a lot from job to job.
Pricing a painting job
Switch to contractor mode to add your labor rate and markup to the paint. Then send the job with the painting estimate template. Many painters price by the room or by the square foot of wall, and the calculator's sq ft figure gives you both.
Questions
How much paint do I need for a 12 × 14 room?
About 2.1 gallons for two coats on the walls with 8 ft ceilings, one door and two windows. Buy 2 gallons and a quart, or 3 gallons if you want extra for touch-ups.
How many square feet does a gallon of paint cover?
Typically 350 to 400 sq ft per coat on smooth, painted walls. Rough or bare surfaces take more paint, closer to 250 to 300 sq ft per gallon.
Is a 5-gallon bucket cheaper than gallons?
Usually, once you need about 4 or more gallons of the same color. Prices vary by store and brand, so enter yours and the calculator picks the cheaper mix.
Do I need two coats of paint?
Usually yes for a color change. One coat can work when repainting the same color over a sound surface.