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Paint Calculator: How Much Paint Do I Need?
Enter your room size to see how many gallons of paint you need for the walls and ceiling, with doors and windows taken out and the number of coats you plan to apply.
How the paint calculator works
The wall area of a rectangular room is its perimeter times its height: 2 × (length + width) × height. We then take out about 21 sq ft for each door (3 × 7 ft) and 15 sq ft for each window (3 × 5 ft), multiply by the number of coats and divide by the coverage on the can.
Example: a 12 × 14 ft bedroom with 8 ft walls has 416 sq ft of wall. Minus one door and two windows leaves 365 sq ft. Two coats is 730 sq ft of painting, and at 350 sq ft per gallon that is 2.1 gallons, so buy 3 gallons (or 2 gallons and a quart).
How far does a gallon of paint go?
Most interior wall paints cover 350 to 400 sq ft per gallon on smooth, primed drywall. Use a lower number, around 250 to 300, for textured walls, bare drywall, brick or stucco, and when you are painting a light color over a dark one. A 5-gallon bucket covers roughly 1,750 to 2,000 sq ft per coat and is usually cheaper per gallon if you need four or more.
Do I need primer?
Use primer on new drywall, patched areas, stained or glossy surfaces, and when you make a big color change. Many "paint and primer in one" products work fine over walls that are already painted in good condition. Primer usually covers about the same area per gallon as paint, and one coat is enough.
Tips for buying paint
- Buy all the paint for one room at the same time so the color batches match, or mix the cans together in a bucket.
- Keep a little left over for touch-ups. Close the lid tightly and store it above freezing.
- Ceilings normally take flat white ceiling paint; trim and doors take semi-gloss. Allow about 1 quart of trim paint for the doors and trim in an average room.
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12 × 12 ft room with 8 ft walls has 384 sq ft of wall. After one door and two windows (about 51 sq ft), two coats need about 1.9 gallons, so buy 2 gallons. Painting the ceiling too adds about 0.8 gallons for two coats.
How many square feet does a gallon of paint cover?
Most interior paint covers 350 to 400 sq ft per gallon on smooth, primed walls. Rough or porous surfaces and big color changes can drop that to 250 to 300 sq ft.
Do I need two coats of paint?
Usually yes. Two coats give even color and better durability. One coat can be enough when repainting the same color over a clean wall.