Estimates only. Check measurements, product labels and local building codes before you buy or build.
How the Paint Calculator works
This calculator answers how many gallons of paint a room needs for the walls, and the ceiling if you include it, for the number of coats you plan, and turns that into gallons and quarts to buy.
Wall area = 2 × (length + width) × wall height, minus doors and windows. Gallons = area × coats ÷ coverage per gallon (350 sq ft by default; use the figure on your can). The ceiling (length × width) is worked out separately because it usually gets a different paint. Each amount is rounded up to whole quarts, and 3 quarts become a gallon, since a gallon usually costs less than three quarts.
Example: a 12' × 10' room with 8' walls, one 3' × 6' 8" door and two 3' × 4' windows, two coats at 350 sq ft per gallon. Walls: 352 − 20 − 24 = 308 sq ft; 308 × 2 ÷ 350 = 1.76 gal, which is 7.04 quarts, so buy 2 gallons. Ceiling: 12 × 10 = 120 sq ft; 120 × 2 ÷ 350 = 0.69 gal, or 2.74 quarts, which rounds to 3 quarts and so becomes 1 gallon. In all you need about 2.45 gallons of paint.
Coverage drops on textured, porous or bare drywall and when covering a dark color, so use the low end of the label's range or add a coat. New drywall should be primed first; figure the primer as its own coat with the primer's coverage. Trim, doors and cabinets are not included.
Frequently asked questions
How much paint do I need for a 12x12 room?
With 8' walls the walls are 2 × (12 + 12) × 8 = 384 sq ft. Two coats at 350 sq ft per gallon: 384 × 2 ÷ 350 = 2.19 gallons, so buy 2 gallons and 1 quart. The 144 sq ft ceiling takes another 0.82 gallon for two coats, so 1 gallon. Subtracting doors and windows brings the wall number down a little.
How many square feet does a gallon of paint cover?
Most interior paints cover about 350 to 400 sq ft per gallon per coat on smooth, primed walls. Textured, porous or unprimed surfaces take more paint, so the calculator starts at 350; change it to the number on your can.
How many coats of paint do I need?
Two coats is the usual plan for walls, and the calculator starts at two. One coat can be enough when repainting the same color over a sound surface; a big color change or new drywall may need primer plus two coats.
Do I subtract doors and windows when calculating paint?
Yes. Enter how many doors and windows the room has; a 3' × 6' 8" door is 20 sq ft and a 3' × 4' window is 12 sq ft, and the sizes can be changed. If you are also painting the doors, figure them separately.