BuildWellHow paint is estimated
Paint is estimated by area and bought by the gallon. Work out the square feet you’re painting, multiply by the number of coats, and divide by how many square feet a gallon covers. The can’s label gives that coverage.
For a rectangular room, the walls are the perimeter times the height: 2 × (length + width) × height. Take out doors and windows, since you won’t be rolling them. The ceiling is length × width, and it’s usually a different paint, so the calculator keeps it separate.
Trim, doors, cabinets and stairs are estimated differently: trim by the linear foot, doors and windows by the each. They usually take a different paint too, an enamel with more sheen. Price them as their own lines.
The paint formulas
- Wall area = 2 × (length + width) × wall height.
- Openings = doors × 21 sq ft (3 × 7 ft) + windows × 15 sq ft (3 × 5 ft).
- Wall paint = (wall area − openings) × coats ÷ coverage per gallon.
- Ceiling paint = length × width × coats ÷ coverage per gallon.
- Gallons to buy = each of those rounded up to a whole gallon.
Most labels list roughly 250 to 400 square feet per gallon per coat. The calculator starts at 350. Use the number on the can you’re buying, and lean lower for rough, porous or textured surfaces.
Paint for common rooms
Two coats on walls and ceiling at 350 square feet per gallon, with one door and two windows.
| Room (8 ft walls) | Walls less openings | Wall paint, 2 coats | Ceiling paint, 2 coats |
|---|---|---|---|
| 10 × 10 ft | 269 sq ft | 1.5 gal → buy 2 | 0.6 gal → buy 1 |
| 12 × 12 ft | 333 sq ft | 1.9 gal → buy 2 | 0.8 gal → buy 1 |
| 12 × 14 ft | 365 sq ft | 2.1 gal → buy 3 | 1 gal → buy 1 |
| 14 × 16 ft | 429 sq ft | 2.5 gal → buy 3 | 1.3 gal → buy 2 |
| 16 × 20 ft | 525 sq ft | 3 gal → buy 3 | 1.8 gal → buy 2 |
How coverage changes the count
Gallons for 1,000 square feet of wall at different label coverages.
| Coverage on the label | 1 coat | 2 coats | 3 coats |
|---|---|---|---|
| 250 sq ft per gallon | 4 gal | 8 gal | 12 gal |
| 300 sq ft per gallon | 3.3 gal | 6.7 gal | 10 gal |
| 350 sq ft per gallon | 2.9 gal | 5.7 gal | 8.6 gal |
| 400 sq ft per gallon | 2.5 gal | 5 gal | 7.5 gal |
The spread is wide. The same 1,000 square feet of wall takes 5 gallons for two coats at 400 square feet per gallon and 8 at 250. The surface, the color change and the paint itself all move it.
Worked examples
A 12 × 12 bedroom
Walls: 2 × 24 × 8 = 384 square feet, less one door and two windows, 51 square feet, leaves 333. Two coats at 350 square feet per gallon: 333 × 2 ÷ 350 = 1.9 gallons, so buy 2 gallons of wall paint. The ceiling is 144 square feet: 144 × 2 ÷ 350 = 0.82, so 1 gallon of ceiling paint.
A 16 × 20 living room, new drywall
The walls are 2 × 36 × 8 = 576 square feet, less 51 for openings: 525. New drywall needs a primer coat before two finish coats. The primer, one coat at 350 square feet per gallon: 1.5 gallons, so 2. The finish, two coats: 3 gallons. The ceiling is 320 square feet: two coats is 1.83 gallons, so 2.
A deep accent color
One 14 foot wall, 8 feet tall, is 112 square feet. A deep color can need three coats to cover evenly: 112 × 3 ÷ 350 = 0.96 gallon, so 1 gallon, with very little to spare. Buy a quart extra for touch-ups if the label coverage is optimistic.
What changes how far paint goes
- The surface. New drywall, bare wood and masonry soak up paint. Primer seals them, so the finish coats cover as the label says.
- Texture. Knockdown, orange peel and popcorn have more surface than flat walls.
- The color change. Going from dark to light, or to a deep color, takes more coats. A tinted primer helps.
- The application. Spraying puts more paint in the air than rolling. Back-rolling after spraying adds labor but evens the finish.
- The paint. Higher-solids paint builds a thicker coat. The label is the guide.
Choosing the sheen
| Sheen | Where it’s usually used |
|---|---|
| Flat or matte | Ceilings, and walls where hiding flaws matters more than washing |
| Eggshell or satin | Most living areas and bedrooms |
| Semi-gloss | Trim, doors, kitchens and bathrooms |
| Gloss | Cabinets, railings and accents that get handled |
The shinier the paint, the more it shows the wall underneath. A glossy finish on a wall with patches and a level 4 drywall finish will show every repair, which is one reason drywall is sometimes taken to level 5 for glossy paint. Higher sheens are easier to wipe clean, which is why they’re used where hands and water are.
Common mistakes
Forgetting the primer. New drywall, patches, stains and big color changes need it. It’s a coat of paint and a coat of labor.
Estimating trim by area. Baseboard and casing are estimated by the linear foot, doors by the each. Painting them takes far more time per square foot than walls.
Buying exactly what the math says. Leave enough for touch-ups after furniture goes back. Keep the leftover, labeled with the room, for the client.
Mixing batches mid-wall. If you need several gallons of a color, box them: pour them together into one bucket so the color is identical.
Leaving out prep. Moving furniture, protecting floors, washing walls, patching and caulking often take as long as the painting.
From gallons to an estimate
A painting estimate is mostly labor. The paint matters, but the hours of prep, cutting in, rolling, trim and cleanup set the price.
Price the extras as their own lines rather than padding the walls. Cutting in, priming, patching and trim each take real time, so a room with a lot of trim or repairs costs more than its wall area suggests. Doors are easiest to price by the each, and trim by the linear foot.
When you estimate painting in BuildWell, describe the rooms and it plans protection, prep, patching, primer, walls, ceilings, trim and doors as separate lines, each with its own labor hours. Paint and supplies are priced at stores near the job, checked within 30 days, and labor at your metro’s painter wage plus your overhead and markup. You can change any line before you send it.
