Paint Coverage Calculator

Coverage depends on the sheen, the porosity of the wall, and how heavily you roll. Flat and eggshell paints cover the most ground, about 350 to 400 sq ft per gallon on smooth primed drywall, because they hide imperfections with a thicker film. Satin and semi-gloss drop to 300 to 350 sq ft because the resin loading is higher. High-gloss enamels cover only 250 to 300 sq ft. Primer falls in the 200 to 250 sq ft range because it is formulated to soak in. The calculator uses the midpoint of each range, so for very rough or unprimed walls drop down to the low end and budget about 15 percent extra.

Two coats is the residential default for three reasons. First, hide: even self-priming paint rarely covers a different underlying color in a single pass, so flashing and lap marks show through. Second, color: pigment dries to a richer, more uniform tone after a second coat because the dry film is thicker and the substrate stops influencing reflectance. Third, durability: two coats double the protective resin layer, which matters in kitchens, bathrooms, and high-traffic hallways. Skip the second coat only when you are repainting the same color over a sound, primed finish.

Reach for a dedicated primer in four situations. Raw drywall absorbs topcoat unevenly and needs a PVA primer to seal the paper. Bare wood, both new and stripped, needs a bonding primer to lock in tannins and stop bleed-through (oil-based on knotty pine, shellac-based on water stains). Glossy surfaces such as old oil-based trim need a bonding primer to give the new latex paint something to grip. Drastic color changes (more than two shades, or any shift to or from a saturated color like red, yellow, or deep blue) need a tinted primer so two finish coats are enough. Self-priming paints handle minor color changes on intact surfaces but do not replace a real primer in any of these four cases.

Use 21 sq ft per standard interior door (a 3 ft wide x 7 ft tall slab) and 15 sq ft per average residential window (a 3 ft x 5 ft single-hung or double-hung). The calculator defaults to those numbers and lets you override them. For French or sliding patio doors use 42 sq ft each. For picture or bay windows measure rough opening width times height and enter the result. Subtracting openings is conservative because you still need to cut in around the trim, so the net wall area should match the area you actually roll, not the gross perimeter times height.

Yes. Buy enough to round up to the next full or half gallon, then add one quart for touch-ups. There are three reasons. Manufacturers tint paint in batches, so a second can ordered two weeks later may not match perfectly even with the same color code. Nail pops, scuffs, and small drywall repairs always happen in the first year, and matched touch-up paint blends better than fresh-tinted replacement. And Murphy's law: a dropped roller, a missed corner, or a thirstier wall than expected can leave you a half-quart short with no easy refill. The calculator already rounds up to the next 0.5 gallon for exactly this reason.