Paint calculator
How many gallons for a room — accounting for coats, ceiling, doors and windows.
Calculator
Detailed breakdown
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How to use this calculator
Measure
Measure the room's length, width and ceiling height in feet, then count doors and windows to deduct.
Calculate
Once you hit calculate, results update as you type. Change any number to compare options instantly.
Order
Print the estimate and take it to your supplier. Quantities are rounded up so you don't come up short.
Getting the gallon count right the first time
Paint coverage is the number everyone gets wrong. A gallon covers roughly 350 square feet per coat on primed, smooth drywall — and that figure falls fast on porous, textured or dramatically different-colored surfaces.
The area calculation is the room perimeter times ceiling height, minus openings. A 12 by 15 foot room with 8 foot ceilings has 432 square feet of wall. Deduct a door and two windows and you are at about 381 square feet. Two coats means 762 square feet of coverage, or roughly 2.2 gallons — which is why you buy three gallons, or two gallons plus a quart for touch-ups.
Round up, always. Running out mid-wall means a trip to the store, and a second can mixed later may not match exactly even from the same formula. Leftover paint is also the only reliable way to touch up scuffs a year from now.
Three situations demand more than the calculator suggests: painting a dark color over light (or the reverse) often needs three coats or a tinted primer; textured or unprimed drywall can drop coverage to 250 square feet per gallon; and sprayers waste noticeably more than rollers. In any of those cases, add 25 percent.
Frequently asked questions
How much paint for a 12x15 room?
About 2.2 gallons for two coats on the walls, deducting a door and two windows. Buy three gallons to have touch-up paint left over.
How many square feet does a gallon cover?
Roughly 350 square feet per coat on primed smooth drywall. Porous, textured or unprimed surfaces can drop that to 250.
Do I need two coats?
Usually yes. One coat rarely covers evenly, especially over a different color. Painting light over dark may need three coats or a tinted primer.
Should I include the ceiling?
Only if you are painting it — ceilings usually get a different flat paint. Switch the dropdown to yes and the calculator adds the floor area.
How much extra should I buy?
Round up to the next gallon. For sprayers, textured walls or big color changes, add about 25 percent.
Sources
Formulas and material assumptions on this page follow published industry guidance: