Paint Calculator
Measure the room once and get the wall area, the gallons to buy for one or two coats, and what it will cost — including a deduction for doors and windows.
Deductions used: 21 sq ft per door, 15 sq ft per window. Texture, porous or bare surfaces can cut coverage by 20–30% — drop the coverage figure rather than adding a fudge factor. Buy all the paint for one room in a single batch: colour can vary slightly between cans, and a mid-wall batch change is visible.
Frequently asked questions
How much paint do I need for a room?
Wall area = perimeter × ceiling height, minus openings. For a 12 × 14 ft room with 8 ft ceilings: perimeter 52 ft × 8 ft = 416 sq ft, minus two doors (about 21 sq ft each) and two windows (about 15 sq ft each) = 344 sq ft of actual wall. Two coats need 688 sq ft of coverage; at 350 sq ft per gallon that is 1.97 gallons — buy 2 gallons, or a gallon plus a quart if you want a little left for touch-ups.
How many square feet does a gallon of paint cover?
Most interior wall paints cover 350–400 sq ft per gallon on a smooth, previously painted surface. Budget closer to 300–350 for new drywall or bare wood, which soak up the first coat, and 250–300 for textured or porous surfaces. The number is printed on the can and it is worth reading — a cheap paint with 250 sq ft coverage can cost more per finished wall than an expensive one at 400.
Do I count doors and windows?
Subtract them, but do not obsess. A standard interior door is about 21 sq ft and a typical window about 15 sq ft. Subtract the big ones and ignore small trim, outlets and switch plates — together they are under 2 sq ft. Painting the door and frame as well? Then add the door area back at roughly 42 sq ft per side including the frame.
Is one coat ever enough?
Only when you are refreshing the same colour in the same sheen on a clean wall. Any colour change — especially light over dark, or a saturated colour over white — needs two coats, and a deep red or navy may need three. Priming first is often cheaper than a third coat of colour, and it stops the old colour from bleeding through. Ceilings almost always need two coats because roller texture leaves thin spots.