Paint Calculator
Find out how much paint to buy for a room, a ceiling or a house exterior, including primer and the number of coats.
How it's calculated
Wall area is the perimeter times the height, minus about 21 sq ft per door and 15 per window. Exterior jobs add the triangular gable ends. Area times coats, divided by the coverage per gallon, gives gallons. The purchase is rounded up to whole quarts.
Worked example
A 14 × 12 ft bedroom with 8 ft ceilings, one door and two windows has 365 sq ft of walls. Two coats at 350 sq ft per gallon is 2.1 gallons: buy 2 gallons and 1 quart, plus about a gallon of ceiling paint.
Field notes
- Coverage on the can assumes smooth, primed surfaces. Bare drywall, patched walls and rough siding take more.
- Prime new drywall, stains and big color changes.
- Box your paint: mix all cans of a color together so there is no color shift between them.
- Cut in and roll one wall at a time to keep a wet edge.
Common questions
- How much does a gallon of paint cover?
- About 350–400 sq ft for one coat on smooth, primed drywall. Rough surfaces get 250–300.
- How much paint for a 12×12 room?
- About 2 gallons for two coats on the walls with 8 ft ceilings, plus a gallon for the ceiling.
- Do I need two coats of paint?
- Usually yes for an even finish, especially when changing colors.