Paint Calculator
How many gallons of wall paint, ceiling paint, and primer you need for a room or several, plus trim paint if you want it.
Why our numbers are more realistic
Most paint calculators multiply wall area by the best-case coverage on the can and stop there. We compared five popular ones with paint makers' own data sheets, and here's where they tend to leave you short:
| Typical calculator | This calculator | Why it matters |
|---|---|---|
| One coverage figure for every wall, usually the best case on the can (350–400 sq ft per gallon) | Coverage depends on the wall: smooth and painted, patched, or new drywall, and smooth or textured | Paint makers say coverage depends on "surface texture and porosity." For a 12×14 room with a door and two windows, two coats on the walls go from 2 gallons at 450 sq ft per gallon to 2 gallons and a quart at 350, both inside the label's own range. On orange-peel or knockdown walls, the same room takes up to 3 gallons. |
| Often no primer line, or primer counted like paint | Adds primer for new drywall, patches, and big color changes, at primer's lower coverage | The drywall maker says to prime new drywall before painting. Primer covers about 200–300 sq ft per gallon, not 350–400. |
| Some leave the ceiling out | Ceiling included by default, as its own line, with extra paint for texture | In a 12×14 room the ceiling adds about 45% to the area you paint, and a textured ceiling soaks up more paint than a smooth one. |
| One room at a time, and some have no way to add doors and trim | Add rooms one by one, and doors, baseboards and casings if you're painting them | One answer for the whole job means one batch of tinted paint. Trim adds up: a 12×14 room's baseboard, one door painted on both sides, and the casings take about 1.5 to 2 quarts over two coats. |
| Answers like "1.83 gallons" | Rounded up to cans you can buy, from the high end of the range | Running out of a custom tint mid-job risks a color mismatch when you reorder. |
How this works
Wall area = room perimeter × wall height, minus 20 sq ft per door and 15 sq ft per window. If you measure by wall area instead, we use your figure and still take off the doors and windows. Gallons = area × coats ÷ coverage per gallon. Coverage is a range, so you see a low and a high amount, and the amount to buy rounds up from the high end.
- Smooth, previously painted walls: 350–450 sq ft per gallon, the range paint makers print on the label.
- Patched walls or new drywall: 300–400 sq ft per gallon, the low end of the label, because porous surfaces soak up more paint. Drywall primer makers give the same 300–400.
- Textured walls and ceilings: coverage cut by 20–30% (a painting-trade estimate; no paint maker publishes one), so roughly 25–40% more paint.
- Primer: 200–300 sq ft per gallon. A full coat on new drywall, a tinted coat on the walls for a big color change, and 15% of the area for spot-priming patches, a planning allowance since patches usually cover only a small part of a wall.
- Several rooms: each room's walls and ceiling are added up, then the doors and windows you counted come off the total.
- Doors and trim: baseboard 6 in tall (0.5 sq ft per foot), each door 20 sq ft a side and painted on both sides, and casings about 5 sq ft per door and 5.5 per window. Trim paint covers about 350–425 sq ft per gallon. We found no paint maker's figure for trim, so the amount is worked out from those sizes.
Sheen, dry time and paint quality
- Sheen: paint makers suggest flat for ceilings, eggshell or satin for bedrooms and living rooms, satin or semi-gloss for kitchens and baths, and semi-gloss for trim and doors. Flatter sheens hide flaws in the wall; glossier ones show them. Sheen names vary by brand, and we don't change coverage by sheen.
- Dry time: wait the recoat time on your can before the second coat, often 1 to 4 hours for latex wall paint and as long as 16 hours for some trim enamels. Label times assume about 77°F and 50% humidity, and labels ask for roughly 50–90°F, so a cold or damp room takes longer.
- Premium paint: it doesn't go farther. One paint maker rates its top line at 350–400 sq ft per gallon and its value line at 400–450. What better paint buys is hide: it can save a coat on a color change, but don't count on it, and still prime new drywall. Use the coverage on your can.
Common questions
How do I figure paint for just one wall?
Choose "Wall area" and enter the wall's width × height. Set doors and windows to 0 if the wall has none, or the default door and two windows come off. A single wall often needs only about half a gallon, but the calculator rounds up to a gallon: two quarts usually cost about as much, and you'll have some left for touch-ups.
Should you paint two coats?
Usually, yes. Paint makers recommend two coats for full color, and two on bare surfaces like new drywall. One coat can do on a repaint in a similar color, which is why the calculator lets you choose.
Why does the ceiling get its own line?
Ceiling paint is usually a separate flat white, so you buy it separately from the wall color.
What this doesn't cover
- Lead paint. If your home was built before 1978, test before sanding or scraping old paint (EPA: epa.gov/lead).
- Crown molding isn't counted on its own. Add its length to the baseboard feet; a typical crown takes about the same paint per foot. Chair rails, stair railings and cabinets aren't counted.
- Cabinets, tile and backsplash in a kitchen or bath. They cover wall you won't paint, so this will buy a little extra. To cut it, measure only the walls you'll paint and use "Wall area".
- Working out the area of vaulted ceilings, gable walls, and stairwells. Measure them as rectangles and triangles, add them up, and use "Wall area".
- Spraying, which uses more paint than a brush or roller.
- Exterior paint, a separate project that wears differently.
Sources
- Benjamin Moore Regal Select technical data sheet: 400–450 sq ft per gallon, depending on surface texture and porosity; two coats on bare surfaces.
- Sherwin-Williams paint calculator guide: paint 350–400 and primer 200–300 sq ft per gallon.
- USG joint compound submittal: prime the entire drywall surface before decorating.
- Sherwin-Williams, "Cover Your Bases": tinted gray primers for deep colors.
- Benjamin Moore At-a-Glance guide: coverage by product line (Aura 350–400, Regal Select and ben 400–450, Advance trim enamel 425–475) and recoat times.
- CompositePaint trim calculator: trim enamel 350–425 sq ft per gallon, baseboard face 0.4–0.5 sq ft per foot, and casing about 5 sq ft per door and 5.5 per window.
- Inch Calculator paint calculator: 20 sq ft per door face.
- Sherwin-Williams sheen guide and Benjamin Moore finish guide: which sheen for which room.
- PPG Speedhide data sheet: recoat time at 77°F and 50% humidity; apply above 50°F.
- Dunn-Edwards guide to paint specs: higher-solids paint gives better hide and fewer coats; coverage and hide are different things.
Numbers last reviewed: October 9, 2026.