Paint Calculator

A standard 12×12 room with 8-foot ceilings needs about 1.5 gallons of paint for two coats on the walls (roughly 384 sq ft of wall area), or about one gallon for a single coat. Always subtract door and window areas, divide the remaining paintable area by 400 sq ft (average coverage per gallon), then multiply by the number of coats. Buy slightly extra for touch-ups and future repairs.

One gallon of paint covers approximately 350 to 400 square feet with a single coat on smooth, primed walls. Coverage drops to 250–350 sq ft on rough, textured, or porous surfaces like stucco, brick, or new drywall. Dramatic color changes often require a second coat, which effectively halves your coverage. This calculator uses 400 sq ft per gallon as the baseline estimate.

Most interior painting jobs need two coats for even color and full coverage. A single coat works only when repainting the same or a very similar color over a clean, primed surface. Plan on a primer coat plus two finish coats when covering bare drywall, making dramatic color changes (dark to light), or painting over stains and glossy surfaces. Two coats means doubling your gallon estimate.

You need primer when painting bare drywall, wood, or metal; covering stains, water damage, or dark colors; or switching from a glossy to a matte finish. Primer is estimated separately from finish paint, at roughly the same coverage rate (about 400 sq ft per gallon). “Paint and primer in one” products can skip a separate primer coat on previously painted surfaces in good condition, but rarely match dedicated primer on problem areas.

To calculate ceiling paint, multiply the room’s length by its width to get the ceiling area, divide by 400 sq ft per gallon, and multiply by the number of coats. A 12×12 ceiling is 144 sq ft — about half a gallon per coat, or one gallon for two coats. Textured ceilings like popcorn or knockdown absorb significantly more paint, so add 20–30% to the estimate.

A typical 2,000 sq ft home interior needs approximately 15 to 20 gallons of paint for walls, ceilings, and trim with two coats. Walls usually account for 10–12 gallons, ceilings 3–4 gallons, and trim and doors 2–3 gallons. The exact amount depends on ceiling height, number of rooms, color changes, and surface texture — calculate room by room for an accurate total.

Measure the height and width of each wall, multiply them for each wall’s area, and add the walls together for total wall area. Subtract the area of doors (about 21 sq ft each) and windows (about 15 sq ft each), since those aren’t painted. Divide the result by 400 sq ft per gallon and multiply by your number of coats. This calculator handles the math automatically once you enter the dimensions.

Yes. Exterior surfaces usually have lower coverage than interior walls because they’re rougher and more porous. Smooth siding covers near the standard 400 sq ft per gallon, but stucco, rough wood, brick, and masonry can drop coverage to 150–250 sq ft per gallon. Exterior jobs also almost always need two coats for weather protection, so reduce your coverage assumption and add a coat when estimating exterior paint.