Paint
Calculator

Most interior latex paints cover 350–400 sq ft per coat per gallon on smooth, primed surfaces. The calculator uses 350 sq ft/gallon as a conservative estimate that accounts for minor texture or porosity. For rough surfaces like brick or stucco, coverage can drop to 200–250 sq ft/gallon. Always check the coverage listed on the paint can label, as formulations vary.

Two coats are standard for most interior painting projects. One coat may be sufficient for touch-ups, same-color repaints, or high-quality paint-and-primer products. Three coats are recommended when making a dramatic color change (e.g., dark to light), painting over stains or previously unpainted drywall, or using thin or low-quality paint. Always apply a primer coat before the first topcoat on bare drywall or bare wood.

This calculator covers walls only. To include the ceiling, calculate ceiling area separately (length × width) and add it to your total. Most ceilings use flat or matte white paint, often sold separately from wall paint. A standard 10×12 room ceiling adds 120 sq ft — roughly one-third of a gallon per coat.

Trim, baseboards, and doors are usually painted with a different product (semi-gloss or gloss) than wall paint. As a rough estimate, budget 1 quart of trim paint per room for baseboards and door/window casings, plus 1 quart per door for both sides. This calculator focuses on wall paint only.

You always round up to whole gallons because you cannot buy a fraction of a gallon at most stores (though quarts are available). Rounding up also gives you a small buffer for touch-ups, mistakes, and any additional coverage needed on heavily textured walls. Save any leftover paint for future touch-ups — label the can with the room, color name, and paint code.

The standard formula is: Wall Area = 2 × (Room Length + Room Width) × Wall Height. Then subtract door area (approx. 21 sq ft per door) and window area (approx. 15 sq ft per window) to get the paintable area. Multiply by the number of coats, then divide by coverage rate (350 sq ft/gal) to get total gallons needed.

Paint alone typically costs $30–$50 per gallon for quality interior paint. A 12×12 room with 8-ft ceilings requires roughly 2 gallons for two coats, so paint cost runs $60–$100. If hiring a painter, labor adds $200–$500+ per room depending on prep work and location. DIY painting is primarily a time investment — budget 4–8 hours for prep and two coats in a standard bedroom.