Room Paint Calculator — How Much Paint Do I Need
Free room paint calculator: enter size, doors and windows to get exact gallons and liters for one room.
Your measurements stay on your device. Nothing is uploaded or stored — the estimate is cleared when you close the tab.Try: Room length=12, Room width=12, Wall height=8, Number of doors=2, Number of windows=2, Coverage per gallon=350, Number of coats=2, Waste factor=10, Surface condition=smooth, Color change=none → 384 sq ft, -72 sq ft, 312 sq ft, 20, 6240 sq ft, 19.61 gal, 20 gallons
How to use
This calculator plans one room from the four numbers that matter: the floor dimensions, the wall height, and the openings you do not paint. It subtracts doors (21 sq ft each) and windows (15 sq ft each) from the gross wall area, then divides by your paint coverage and multiplies by the coats you choose.
A 10 to 20 percent waste allowance is built in so you do not run short on a second coat. If you select new drywall, textured walls, or a dark-to-light color change, the tool also estimates primer and adds the extra top coat those jobs need. The result is rounded up to whole gallons, because paint is sold that way.
Use the quick tips below, then scroll to the frequently asked questions for common room sizes and coat rules.
FAQ
How much paint do I need for a 12x12 room?
A 12 ft by 12 ft room with 8 ft ceilings has about 384 sq ft of wall before openings. Subtract two doors and one window (about 57 sq ft) and you get roughly 327 sq ft of net wall. At 350 sq ft per gallon and two coats with 10 percent waste, plan on about 2 gallons of paint. The calculator above does this automatically for any size.
How many coats of paint do I need?
Two coats are standard for even, opaque coverage on a repainted wall. A dark-to-light color change often needs a third coat or a tinted primer first. New drywall or bare wood needs primer plus two top coats. The calculator adds the extra coat automatically when you pick a color change.
How do I subtract doors and windows?
Count each door as 21 sq ft and each window as 15 sq ft of wall you do not paint. A room with two doors and three windows therefore skips about 87 sq ft. Enter the counts above and the tool removes them from the gross wall area before dividing by coverage.
What coverage should I use?
Most latex wall paint covers 350 to 400 sq ft per gallon on smooth, repainted walls. Textured or new drywall absorbs more, so use 250 to 300. Check the label on your can; the calculator lets you set the exact number.
Do I need primer?
Primer is recommended on new drywall, bare wood, stained or glossy surfaces, and for dramatic color changes. On previously painted smooth walls, two top coats usually work without primer. See the primer, ceiling and trim calculator for a combined estimate.
Why buy about 10 percent extra?
A 10 percent waste allowance covers touch-ups, roller drag, and small coverage differences between brands. Running out mid-project means a second trip and possible color-match trouble on a fresh batch.