How much does a gallon of paint cover?

About 350 to 400 square feet in one coat on a smooth, primed wall. Textured, porous or dark-over-light surfaces take more; the can prints its own figure.

How many gallons for a 12 × 14 room?

Walls are about 380 sq ft after one door and two windows; two coats is 760 sq ft, so 2.2 gallons: buy three, or two gallons plus a quart.

Do I subtract windows and doors?

Yes, this sheet does: 21 sq ft per door and 15 per window, the usual estimating allowances. Trim and doors themselves are painted separately, usually a quart per door.

Paint calculator

Form 40 · Materials estimateFigures checked 2026-09-04

US customary

Measurements

Room length(ft)

Room width(ft)

Wall height(ft)

Rooms this size

Doors21 sq ft each

Windows15 sq ft each

What you need

Quantity · Amount

01Wall area, openings deducted2 × (12 + 14) × 8 ft − 1 doors − 2 windows365 sq ft
02Ceiling area12 × 14 ft168 sq ft
03Paint, 2 coats350 sq ft per gallon per coat; buy 4 gal3.1 gal$180

Total, paint$180

Buy in gallons, not quarts, above two quarts: it is cheaper and the colour is mixed in one batch.
Deep colours over white, and any colour over bare drywall, need the primer coat to cover in two.

The material

Paint the ceiling

YesNo

Primer coat

NoYes

Coats

Coverage(sq ft)Printed on the can: 350–400 sq ft per gallon per coat

Prices — put in what you were quoted

Paint price($ per gallon)Interior wall paint $30–70 per gallon

Total, paint4 gallons of paint$180

Where these figures come from

Spread rate 350 sq ft per gallon per coat: the usual manufacturer figure for interior latex on a smooth primed surface.
Door 21 sq ft and window 15 sq ft: standard estimating allowances.
Prices are typical US retail figures at the date on this sheet.

Type the room's length, width and wall height, and how many doors and windows to take off. The sheet works out the wall area, divides by the spread rate (350 sq ft per gallon, one coat), multiplies by the number of coats, and adds the ceiling and primer if you want them.

Worked examples

Bedroom 12 × 14 ft, 8 ft walls, two coats: 3.1 gal — paint, 2 coats, about $180 in paint.
Whole floor: four rooms 12 × 12: 11 gal — paint, 2 coats, about $495 in paint.

How it is worked out

Wall area = 2 × (length + width) × height − 21 per door − 15 per window. Add length × width for the ceiling. Gallons = area × coats ÷ the spread rate. Primer = area ÷ spread rate, one coat.

The figures behind it

Spread rate 350 sq ft per gallon per coat: the usual manufacturer figure for interior latex on a smooth primed surface.
Door 21 sq ft and window 15 sq ft: standard estimating allowances.
Prices are typical US retail figures at the date on this sheet.

Every figure here is an estimate. Materials vary with moisture, compaction and product; order a little extra and confirm quantities with your supplier.

Questions people ask

How much does a gallon of paint cover?: About 350 to 400 square feet in one coat on a smooth, primed wall. Textured, porous or dark-over-light surfaces take more; the can prints its own figure.
How many gallons for a 12 × 14 room?: Walls are about 380 sq ft after one door and two windows; two coats is 760 sq ft, so 2.2 gallons: buy three, or two gallons plus a quart.
Do I subtract windows and doors?: Yes, this sheet does: 21 sq ft per door and 15 per window, the usual estimating allowances. Trim and doors themselves are painted separately, usually a quart per door.

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