Everyday
Paint Calculator
Figure out how much paint a room really needs: wall area minus doors and windows, ceilings and trim, primer separate, rounded up to the cans stores actually sell.
How it works
Behind the numbers
Wall area comes from the room's perimeter times its height, minus a standard allowance for each door (21 sq ft) and window (15 sq ft). Add more rooms and the areas accumulate, so a whole apartment or house can be estimated in one pass. Ceilings add length times width per room, and baseboards add a six-inch strip around each room's perimeter, both optional.
Finish paint equals the total paintable area times the number of coats, divided by the coverage rate from your can. The default of 350 sq ft per gallon matches most interior latex paints; adjust it to the number printed on your can. Primer gets its own calculation with its own coverage, because it spreads differently on bare drywall, and it skips the trim.
The buy list rounds up to whole store cans: quarts, gallons, and 5-gallon buckets, picking the smallest combination that covers the job. A metric mode switches everything to square meters and liters with equivalent can sizes. Prices are editable so the cost estimate can match your local store; they are starting defaults, not quotes.
FAQ
Questions, answered
How much paint do I need for a 12x12 room?
A 12x12 room with 8-foot ceilings has about 384 sq ft of wall. Minus a door and two windows (51 sq ft), two coats at 350 sq ft per gallon needs about 1.9 gallons of finish paint, so buy two gallons. The calculator above does this from your exact dimensions.
How many square feet does a gallon of paint cover?
Most interior latex paints cover 350 to 400 sq ft per gallon for one coat; the can label states the exact figure. Primer usually covers less on bare drywall, around 250 to 300 sq ft per gallon. Enter the label numbers for an accurate estimate.
Do I need primer?
On bare drywall, patched spots, or dramatic color changes, yes: primer seals the surface and usually means one less finish coat. On previously painted walls in good shape, two finish coats are typically enough without primer.
Should I buy extra paint?
The buy list already rounds up to whole cans, which leaves a small surplus for touch-ups. Keep the leftover sealed and labeled; a quart of the exact color and sheen is worth more than any color match later.