How many gallons of paint for a 12 × 10 room?

With 8 ft ceilings the walls total 352 square feet, so two coats at 350 square feet per gallon need 3 gallons. Subtract one door and two windows (about 50 square feet) and two coats fit in 2 gallons.

How much does one gallon of paint cover?

Roughly 350 square feet per coat for typical interior latex on smooth, primed walls — product data sheets quote 350–400. Textured or porous surfaces cover noticeably less.

Should I subtract doors and windows from the wall area?

Yes — about 20 square feet per door and 15 per average window. On a small room that subtraction often saves a whole can, since gallons round up at every can boundary.

Square Footage Calculator

Square Footage Calculator — Paint Coverage Calculator

The gallons view: enter wall area, coats, and a coverage rate and it rounds up to the whole cans you must actually buy. A 12 ft × 10 ft room with 8 ft ceilings has 352 square feet of wall (44 ft of perimeter × 8 ft), and two coats at the conventional 350 square feet per gallon is 704 square feet of coverage — 3 gallons, because paint is sold by the can, not the ounce.

Square footage

EstimateWall area (sq ft)CoatsCoverage per gallon (sq ft)

Paint to buy

3 gallons

rounded up to whole cans — paint is sold by the gallon

Breakdown

Coverage needed (sq ft)704

Area is plain arithmetic on the dimensions you enter; flooring and paint use the waste and coverage assumptions shown above. A planning estimate — not a quote, bid, or appraisal.

Wall area is perimeter × ceiling height

Add up the wall lengths around the room (the perimeter) and multiply by the ceiling height. A 12 ft × 10 ft room has 2 × (12 + 10) = 44 ft of perimeter, which under 8 ft ceilings is 352 square feet of paintable wall. Then subtract what does not get painted: about 20 square feet per door and about 15 square feet per average window is the usual allowance. With one door and two windows, the 352 drops to 302 square feet — and two coats now need 2 gallons instead of 3, a full can saved by thirty seconds of subtraction.

The ceiling is its own job: it is the floor area (120 square feet in the 12 ft × 10 ft example), usually painted in a dedicated ceiling paint, so estimate it as a separate run of the calculator rather than folding it into the wall number.

Coats, primer, and when one gallon is not enough

Two coats is the standard for color changes and for a uniform, washable finish; one coat only works when refreshing the same color on walls in good condition. The whole-can rounding bites either way: even a single coat on 352 square feet needs 2 gallons, because 352 already exceeds what one 350-square-foot gallon covers. That cliff at each can boundary is why the calculator reports gallons to buy rather than a decimal that no store will sell you.

Primer is a separate product with its own coverage rate, needed over bare drywall, patches, stains, or when going light-over-dark — run it as its own estimate at one coat. And keep the coverage input honest: rough or porous surfaces can fall well below the 350 square feet per gallon convention, and dropping the rate is the cheap insurance against a second trip to the store.

Questions

How many gallons of paint for a 12 × 10 room?: With 8 ft ceilings the walls total 352 square feet, so two coats at 350 square feet per gallon need 3 gallons. Subtract one door and two windows (about 50 square feet) and two coats fit in 2 gallons.
How much does one gallon of paint cover?: Roughly 350 square feet per coat for typical interior latex on smooth, primed walls — product data sheets quote 350–400. Textured or porous surfaces cover noticeably less.
Should I subtract doors and windows from the wall area?: Yes — about 20 square feet per door and 15 per average window. On a small room that subtraction often saves a whole can, since gallons round up at every can boundary.