Paint calculator: how much paint do I need for a room?
Measure the room, count the doors and windows, and get how many gallons to buy. Most wall paint covers about 350 square feet per gallon per coat; check the label on the can you're buying.
- Doors and windows
- Ceiling option
- Buy-ready amounts
Doors count as about 20 sq ft and windows about 15 sq ft. Rough patches, dark colors or bare drywall can need more; primer is extra. Doing a whole room? The room materials calculator gives paint, flooring, baseboard and drywall from one set of measurements.
Before you paint
How it works
Wall area = 2 × (length + width) × height, minus about 20 square feet per door and 15 per window. The ceiling, if you include it, adds length × width.
Gallons = area × coats × texture factor ÷ coverage per gallon. Coverage defaults to 350 square feet, a typical label figure; change it to match your can. Light texture adds 10% and heavy texture or rough surfaces add 20%, since they soak up more paint.
Primer, if you check it, is one coat at about 300 square feet per gallon, a common figure on primer labels, with the same texture factor.
What to buy rounds up to whole gallons plus quarts, and three quarts or more becomes another gallon, since it's usually cheaper.
About this tool
Who it's for
For anyone about to buy paint and hoping not to make a second trip.
Example
You enterA 12x12 room, 8-foot walls, one door, two windows, two coats
You getAbout 1.9 gallons, so buy 2.
What's different
- Subtracts doors and windows, and adds the ceiling if you want.
- Rounds to what you can actually buy, like gallons plus quarts.
- Uses your can's coverage number if it's different.
Gotchas and tips
- Dark colors, rough walls and bare drywall take more.
- Primer is separate.
- Buy it all at once so the batch matches.
Privacy: Runs entirely in your browser. Nothing you type is sent to us, and anything it remembers is saved on this device only.
Built and maintained by the GrabTheHammer team, using the same time, cost and safety notes as our guides. Updated November 2026. Spot a problem? Tell us.
Paint questions
How much paint do I need for a 12x12 room?
With 8-foot walls, one door and two windows, a 12x12 room has about 330 square feet of wall. Two coats at 350 square feet per gallon comes to just under 2 gallons, so buy 2.
Do I really need two coats?
Usually, yes. Two coats give even color and hide roller marks, especially over a different color or on patched walls. Paint-and-primer products sometimes cover in one over a similar color.
Should I buy extra paint?
Keep a little leftover for touch-ups later. Paint from the same batch matches best, so buying enough at once helps.