Paint quantity depends on surface area, coverage, number of coats, texture, and application method. A room's floor area alone is not enough to estimate wall paint.
Measure the surfaces
For each wall, multiply width by height and add the areas. Subtract large doors and windows when their size is known. Ceilings are a separate surface with their own area.
Apply coverage and coats
Divide the total paintable area by the product's stated coverage, then multiply for the number of coats. Rough, porous, dark, or previously unpainted surfaces can use more paint than a smooth primed wall.
Buy with the finish in mind
Keep a small amount for touch-ups and mix cans if color matching matters. Check the label for coverage, drying, recoat, and primer guidance rather than relying on a generic rule.
A worked example
Worked example: four walls each 12 feet wide and 8 feet high create 384 square feet before subtracting openings. Divide by the label coverage and multiply by the planned coats.
Keep primer and trim separate from the wall calculation. Rough surfaces and strong color changes can reduce real coverage below the label's ideal figure.
Keep the same paint product and application method in the estimate. A roller, sprayer, brush, porous substrate, or dramatic color change can make the label coverage an optimistic ceiling.
Keep leftover paint labeled with the room and finish; a small reserve can prevent a later mismatch when a wall needs repair.
Accurate measurements and the product label beat a floor-area shortcut when planning paint.
COMMON QUESTIONS
Frequently asked questions
Should windows be subtracted?
Subtract large openings when their area is known; small openings may not justify the measuring effort.
Does one coat always cover?
No. Color, surface, primer, and paint type can make a second coat necessary.