Interior Paint Calculator
Enter your room size, take out the doors and windows, and choose how many coats. You get the paint needed in gallons and liters, how many cans to buy, and the cost - updated live as you type. Add a primer coat or the ceiling if you need them. Nothing uploaded.
Breakdown
Learn more: estimating interior paint
How the paint estimate is built
The calculator finds your wall area from the room shape: perimeter is 2 x (length + width), and gross wall area is perimeter x wall height. It then subtracts every door and window you list. The leftover is the paintable area. Multiply that by the number of coats and divide by the coverage per gallon to get the volume of paint. For example, a 12 by 10 foot room with 8 foot walls has a 44 foot perimeter and 352 square feet of wall; remove a 3 by 7 door and two 3 by 4 windows (45 square feet total) and 307 square feet remain.
Coats, primer, and surface texture
Two finish coats is the usual choice for a clean, even result. A primer coat is worth adding over bare drywall, filler, stains, or a strong color change, and it is counted on its own line because primer covers a little less per gallon than finish paint (about 300 versus 350 square feet). Texture matters too: smooth walls take paint at the rated coverage, while light texture drops it about 10 percent and heavy texture, popcorn, or rough masonry about 22 percent. So the 307 square foot room above needs about 1.75 gallons of finish paint smooth, but closer to 2.25 gallons on heavy texture.
Cans to buy and cost
Paint is sold in fixed sizes, so the raw gallon figure is rounded up to whole cans of the size you pick - gallon cans, quarts, or 5 gallon buckets. The 1.75 gallon example rounds up to two 1 gallon cans. Cost is simply the number of cans times the price per can, including any separate primer cans. Buying one extra small can for touch-ups is common, since color-matched paint is hard to reproduce later.
FAQ
How much paint do I need for one room?
Multiply the wall perimeter by the wall height to get gross wall area, then subtract the area of doors and windows. A 12 by 10 foot room with 8 foot walls has a 44 foot perimeter and 352 square feet of wall. Taking out one door (21 sq ft) and two windows (24 sq ft) leaves 307 square feet. Two coats at 350 sq ft per gallon is 307 x 2 / 350 = about 1.75 gallons, so you buy two gallon cans.
How many coats of paint should I use?
Two coats is standard for most interior walls and gives even color and coverage. Use one coat only when repainting the same color over a sound surface. Add a primer coat when covering bare drywall, patches, stains, or a big color change. This calculator counts primer separately because primer covers slightly less area per gallon than finish paint.
Do textured walls need more paint?
Yes. Rough surfaces hold more paint, so the effective coverage per gallon drops. This calculator lowers coverage by about 10 percent for light texture and about 22 percent for heavy texture, popcorn, or rough masonry. The same 307 square foot room that needs 1.75 gallons smooth needs closer to 2.25 gallons on a heavily textured surface.