Paint coverage calculator

Paint coverage calculator — gallons, coats, and cost for any room

Paint is one of those materials where buying the right amount matters for two different reasons: buy too little and you can't finish — color-matched mid-project paint rarely matches exactly, and running out mid-wall is a disaster. Buy too much and you have gallons of a custom-matched color you'll never use. The math is fast once you know your surface area and your product's coverage rate.

What affects coverage rate

The coverage rate printed on a paint can is the theoretical spread rate on a smooth, non-porous surface. Real walls are not that. Factors that reduce actual coverage:

• Surface porosity — bare drywall, new plaster, and unprimed wood absorb the first coat heavily. Expect 200–250 sq ft/gal on bare surfaces even with a thick primer.
• Surface texture — orange peel, knockdown, and heavy texture patterns have more surface area than a flat wall. A heavy orange peel can reduce effective coverage by 15–25%.
• Sheen level — glossier paints have more binders and resins, less pigment volume, and lower coverage. Flat matte covers best; high gloss covers worst.
• Color depth — deep tones and saturated colors require more pigment, which slightly reduces coverage. Extremely dark colors (navy, charcoal, deep red) often need 3 coats to achieve full opacity.

Sheen guide — which finish for which surface

• Flat / matte (coverage ~400 sq ft/gal) — ceilings and living room walls in low-traffic areas. Hides surface imperfections best. Not washable — mark and scuff easily.
• Eggshell (coverage ~380 sq ft/gal) — most popular interior wall finish. Slight sheen, reasonably washable, forgiving on imperfect walls. Good for bedrooms and living areas.
• Satin (coverage ~350 sq ft/gal) — kitchens, bathrooms, kids' rooms, hallways. More washable than eggshell, slightly more reflective. Highlights surface imperfections more.
• Semi-gloss (coverage ~300–350 sq ft/gal) — trim, doors, cabinets, and bathroom walls. Very washable, durable, moisture-resistant. Telegraphs every imperfection — surfaces must be sanded smooth before painting.
• High gloss (coverage ~300 sq ft/gal) — furniture, cabinets, exterior trim. Maximum durability and washability. Requires perfect surface prep.

One coat vs. two coats — the honest answer

Most residential painting specs call for two finish coats over primer. One coat is a corner cut that usually shows: in certain lighting conditions you can see the substrate color telegraphing through, or the coverage is uneven at the edges. Two coats give true, even opacity.

When two coats become three: going from white to a very saturated color (deep red, dark navy, hunter green) often requires three coats because the pigment density in these colors is lower — they need multiple layers to achieve full opacity. Tinting your primer to 50% of the finish color can eliminate the need for a third coat.

Buying in bulk: gallon vs. 5-gallon bucket

A 5-gallon bucket of standard interior paint typically costs $130–$180 (about $26–$36/gallon), while individual gallons run $40–$55/gallon. If your project requires 4 or more gallons of the same color, the 5-gallon bucket saves $50–$80 and ensures perfect color consistency — no risk of dye lot variation between separate gallon cans. If you need 2–3 gallons in a custom-matched color, buy all at once from the same batch and write the formula on the can lid.

Paint for trim and doors

This calculator covers wall area only. Doors, trim, baseboards, and window casings are typically painted separately in a different sheen (semi-gloss or gloss). A rough estimate: one quart of trim paint per door (both sides plus jamb); one gallon covers approximately 200 linear feet of 3.5-inch baseboard. Budget for trim paint separately from your wall calculation.