Understanding your result
The headline is the ceiling paint for the coats you chose, with the allowance, and the sub-line is what to buy. The three figures show the ceiling area, the real coverage after the texture factor, and the cans. The real coverage is worth a glance: it is the can’s figure multiplied by 1.0 for smooth, 0.8 for light texture and 0.6 for heavy texture or popcorn, and it is why the quantity can be much larger than a flat division suggests.
A ceiling’s area is simply length times width, so there is no openings line as there is in the wall paint calculator. Skylights and large light fixtures are small enough to ignore. If the ceiling is sloped or vaulted, measure along the slope rather than across the floor, or the calculator will under-count.
Ceiling paint is rarely the expensive part of a room, but it is the part people run out of halfway, because a gallon that would do two coats on a smooth ceiling does only one on popcorn. If the quantity comes out just over a round number, buy the extra quart. The paint cost calculator prices the result, and the spray versus roll calculator shows how much more a sprayer uses if you are considering one for a heavily textured ceiling.
How we calculate this
The texture factor is the whole difference between this and a generic calculator. A sprayed-on texture roughly doubles the surface area at the scale of a roller fibre, and the paint has to fill the hollows before it covers the peaks. The factors of 0.8 and 0.6 are the mid-points of what manufacturers’ data sheets imply when they quote a lower coverage for “rough or porous surfaces”, and the coverage rates table lists those figures by product. If your can gives its own textured figure, enter it as the coverage and set the texture to smooth.
The coverage default of 400 sq ft per gallon is what flat ceiling paints typically print for a smooth, previously painted surface. Bare drywall on a new ceiling absorbs more; prime it, or drop the coverage to 300. Everything after the area and the coverage is the same arithmetic the paint coverage calculator does for any surface.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Coverage, smooth ceiling | 400 sq ft per gallon (9.8 m²/L) | The upper end of the 350–400 sq ft per gallon printed on flat ceiling paint data sheets (Benjamin Moore, Sherwin-Williams, Behr); ceiling paint is applied slightly thinner than wall paint |
| Light texture factor | 0.8 | Orange peel and knockdown: the lower coverage manufacturers quote for lightly textured surfaces, expressed as a share of the smooth figure |
| Heavy texture / popcorn factor | 0.6 | Acoustic and heavy textures: the “rough or porous” coverage on the same data sheets, typically 200–250 sq ft per gallon |
| Coats | 2 | A colour change or a yellowed ceiling; one coat for a same-colour refresh |
| Allowance | 5% | Roller loss and a touch-up jar |
Assumptions last reviewed October 7, 2026.
The calculator does not model a never-painted popcorn ceiling, which can absorb the first coat almost completely and may need to be sprayed rather than rolled, nor stain blocking, which is a primer question. The textured ceilings guide covers both, with the nap sizes and the technique that keep the texture on the ceiling rather than in the tray.
Two worked examples
A 12 × 12 smooth ceiling, two coats
The default case: a bedroom ceiling, previously painted, going from an off-white to a bright white.
- Area: 12 × 12 = 144 sq ft
- Real coverage: 400 × 1.0 = 400 sq ft per gallon
- Per coat: 144 ÷ 400 = 0.36 gallons
- Needed: 0.36 × 2 × 1.05 = 0.76 gallons, or 3.02 quarts
- Buy: 1 gallon, with about a quart left over
Three quarts would cover it, but three quarts cost about as much as a gallon and leave nothing for touch-ups, so a gallon is the sensible buy.
A 20 × 15 popcorn ceiling, two coats
A family room with an acoustic ceiling that has never been repainted well.
- Area: 20 × 15 = 300 sq ft
- Real coverage: 400 × 0.6 = 240 sq ft per gallon
- Per coat: 300 ÷ 240 = 1.25 gallons
- Needed: 1.25 × 2 × 1.05 = 2.63 gallons
- Buy: 2 gallons + 3 quarts (2.75 gallons), half a quart over
The same ceiling smooth would need 1.58 gallons. The texture adds a full gallon, and a 3/4 in nap roller to carry it. A 14 × 16 ft knockdown ceiling given one coat of one-coat ceiling paint, for comparison, is 224 sq ft at 320 sq ft per gallon: 0.7 gallons per coat, 2.94 quarts with the allowance, three quarts to buy.
Where to find your inputs
Length and width. The room’s floor dimensions, wall to wall, unless the ceiling is sloped: then measure the sloped length with a tape or use the square footage of the slope from a plan. A tray ceiling has a flat centre and four sloped sides; add them up and use the area mode.
Texture. Run a hand over it. Smooth is flat drywall; orange peel feels like its namesake; knockdown has flattened splatters; popcorn is the crumbly acoustic finish common before the 1990s. If a popcorn ceiling was installed before 1978 it may contain asbestos, and sanding or scraping it is a job for a licensed abatement contractor, not a paint question.
Coverage. From the can or the technical data sheet, using the figure for a smooth surface and letting the texture setting do the rest. Do not apply the texture twice.
Coats. Two for a colour change or a yellowed ceiling, one for a same-colour refresh with a one-coat product. Stains are a primer question, not a coats question.
Common mistakes
- Using the wall paint’s coverage on a textured ceiling. The texture can take 40% more paint. Set the texture or lower the coverage.
- Rolling a dry popcorn ceiling hard. The texture comes off in the roller. Use a thick nap, light pressure and one pass; spray if you can.
- Painting over water stains. They bleed through flat paint within weeks. Spot-prime with a stain blocker first.
- Choosing eggshell or satin for a ceiling. Sheen shows every lap mark under raking light. Flat hides them.
- Doing the walls first. Ceiling spatter lands on fresh wall paint. Ceiling first, then walls, then trim.
- Measuring the floor of a room with a vaulted ceiling. The sloped surface is larger than the floor; measure the slope.
Questions people ask
- How much paint does a 12 × 12 ceiling need?
- 144 sq ft of smooth ceiling at 400 sq ft per gallon takes 0.36 gallons per coat. Two coats with a 5% allowance is 0.76 gallons, just over three quarts, so a single gallon covers it with about a quart to spare.
- How much more paint does a popcorn ceiling take?
- Roughly two-thirds more. The calculator cuts the can's coverage to 60% for heavy texture or popcorn, so 400 sq ft per gallon becomes 240. A 20 × 15 ft popcorn ceiling takes 2.63 gallons for two coats where a smooth one would take 1.58.
- Is one coat of ceiling paint enough?
- Over the same colour on a sound, clean ceiling, with a paint sold as one-coat ceiling paint, usually yes. Over a yellowed or patched ceiling, or when changing from an off-white to a bright white, it is not. Water stains need a stain-blocking primer; no number of coats of ordinary paint will hide them for long.
- Can I use leftover wall paint on the ceiling?
- You can if it is flat or matt. Satin and eggshell wall paints show every roller lap and every imperfection in the drywall when light rakes across a ceiling. Dedicated ceiling paint is flat, slightly thicker so it spatters less, and usually cheaper.
- What roller nap for a ceiling?
- 3/8 in for a smooth ceiling, 1/2 in for light texture, 3/4 in or more for popcorn. A thicker nap holds more paint, which is why textured ceilings use more per square foot. The paint fills the texture rather than lying on top of it.
- Should I paint the ceiling before the walls?
- Yes. Ceiling first, then walls, then trim, so each stage covers the overspray and roller spatter of the one before. The painting-a-room guide sets out the order and the drying time between stages.