Paint quantity depends on the area being painted, the number of coats, and the coverage listed for the exact paint. A room’s floor area alone does not tell you how much wall paint to buy. Ceiling height, room perimeter, doors and windows, surface texture, primer, and color change can all affect the result.
Measure walls and ceiling separately
For four walls in a rectangular room, multiply the room perimeter by ceiling height. Add ceiling area only if you plan to paint it. Subtract large doors or windows if measured; smaller openings may not save paint once cutting in, touch-ups, and remaining paint are considered.
wall area = 2 × (room length + room width) × ceiling height ceiling area = room length × room width paint gallons = (paintable area × coats) ÷ label coverage per gallon
Example: a 12-by-12-foot room with 8-foot walls has 384 square feet of wall area. If you paint the ceiling too, add 144 square feet for 528 square feet total. At a hypothetical label coverage of 350 square feet per gallon, one coat is 528 ÷ 350 = 1.51 gallons. Two coats would be about 3.02 gallons before rounding to available can sizes.
| Paintable area | One coat | Two coats |
|---|---|---|
| 384 sq ft | 1.10 gal | 2.19 gal |
| 528 sq ft | 1.51 gal | 3.02 gal |
| 700 sq ft | 2.00 gal | 4.00 gal |
Use the can’s coverage as the starting point
Coverage on a label is an estimate under stated conditions. A rough or porous surface, unpainted drywall, strong color change, or application method may require more material or primer. The required coat count depends on the product, surface, and desired finish. Read the technical data sheet and label; do not assume every paint covers identically.
Plan for touch-ups and consistent color
Round purchases to the package sizes available and consider keeping a small amount for future touch-ups, especially if the color is custom mixed. For multiple cans of the same color, mixing them together before application can help reduce subtle differences between batches. Follow the paint manufacturer’s advice for storage and cleanup.
Enter your room dimensions and the coverage printed on the can in the paint calculator. Add separate walls or rooms if they have different heights, colors, or surfaces.
Frequently asked questions
How much paint do I need for a 12×12 room?
With 8-foot walls, the room has about 384 sq ft of wall area, or 528 sq ft including the ceiling, before openings. Divide the paintable area by label coverage and multiply by the number of coats.
How many coats of paint should I plan for?
Follow the paint label and account for surface preparation, existing color, and desired finish. The calculator multiplies by the coat count you enter.
Should I subtract doors and windows?
Large measured openings can be subtracted from the wall area. Small openings may not meaningfully reduce the purchase because of cutting-in and touch-up needs.
Does one gallon always cover 350 square feet?
No. Coverage varies by product and surface conditions. Use the coverage stated for your specific paint and confirm with the manufacturer’s product information.
These guides explain estimates and planning arithmetic, not a substitute for product instructions, approved plans, professional advice, or local requirements. Read how our calculations work.