Guide
How Much Paint Do I Need for a Room or a House?
Wall area is perimeter times ceiling height, minus doors and windows. Divide by about 350 sq ft per gallon and multiply by coats. Room-by-room example.
Updated · FloorFigures
Short answer
Wall area = perimeter × ceiling height − doors and windows. Multiply by the number of coats (usually 2) and divide by 350–400 sq ft per gallon, the range Sherwin-Williams gives. A 12' × 12' room with 8 ft ceilings, one door and one window has 348 sq ft of wall: two coats take 1.99 gallons, so buy 2 gallons.
Paint math is simple once you have the wall area, and the wall area comes straight from the room sizes. Here is how to work it out for one room or a whole house, how many coats to plan for, and what to buy for ceilings and trim.
- 1
Find the perimeter
Add up the wall lengths. For a rectangle that's 2 × (length + width): a 12' × 12' room has 48 ft of wall. - 2
Multiply by the ceiling height
48 ft × 8 ft = 384 sq ft of gross wall area. - 3
Subtract doors and windows
Take off each opening's width × height. One door and one window: 384 − 21 − 15 = 348 sq ft. - 4
Multiply by coats, divide by coverage
348 × 2 coats ÷ 350 sq ft per gallon = 1.99 gallons. Round up to 2.
How do I calculate wall square footage minus doors and windows?
Perimeter × height gives the gross wall area. Sherwin-Williams advises subtracting the actual openings, so measure each door and window if you can. When you only know how many there are, our wall area calculator uses 21 sq ft per door and 15 per window.
| Opening | Size | Area to subtract |
|---|---|---|
| Interior door | 3'0" × 6'8" | 20.0 sq ft |
| Door (calculator default) | 3' × 7' | 21 sq ft |
| Window (calculator default) | 3' × 5' | 15 sq ft |
| Pair of doors or a slider | 6'0" × 6'8" | 40.0 sq ft |
Measuring room by room counts both faces of every interior wall, which is right: each face gets its own paint. In kitchens, also subtract wall hidden behind upper cabinets and backsplash if you want a tight number.
How much does a gallon of paint cover?
| Product | Coverage per gallon, one coat | Source |
|---|---|---|
| Interior paint, typical | 350–400 sq ft | Sherwin-Williams |
| Primer | 200–300 sq ft | Sherwin-Williams |
| Behr Premium Plus Interior Flat | 250–400 sq ft | Behr |
Plan on 350 sq ft per gallon, the low end of the usual range. Rough, porous or textured surfaces soak up more, and so does covering a much darker color. The label on the can gives the figure for that product.
How many coats of paint do I need?
Plan on two. Benjamin Moore's paint calculator assumes 2 coats, and two coats is the usual standard for an even finish. A single coat can be enough when you're refreshing the same color over a sound wall. New drywall, patched areas and stains need primer first, and a big color change may need primer or a third coat. Coats multiply the paint: gallons = wall area × coats ÷ coverage.
How much paint for a ceiling?
A flat ceiling has the same area as the floor, length × width. A 12' × 12' ceiling is 144 sq ft: two coats is 288 ÷ 350 = 0.82 gallons, so 1 gallon. Benjamin Moore's calculator leaves the ceiling out, so add it separately, and buy it separately if you use a ceiling paint. A sloped or vaulted ceiling has more surface than the floor below it, so measure along the slope.
How much paint for trim and doors?
Trim is measured in linear feet and adds up to little area. A quart is a quarter gallon, about 87 sq ft per coat at 350 sq ft per gallon. A 3'0" × 6'8" door is 20 sq ft a side, so both sides with two coats is 80 sq ft, roughly a quart before the edges and casing. Trim and doors are often painted in a different sheen, so they're usually a separate purchase.
Example: how much paint for a small house?
Six rooms with 8 ft ceilings, doors at 21 sq ft and windows at 15 sq ft:
| Room | Size | Perimeter | Doors / windows | Walls | Ceiling |
|---|---|---|---|---|---|
| Living room | 16' × 14' | 60 ft | 2 / 2 | 408 sq ft | 224 sq ft |
| Kitchen | 12' × 10' | 44 ft | 1 / 1 | 316 sq ft | 120 sq ft |
| Bedroom 1 | 12' × 12' | 48 ft | 2 / 2 | 312 sq ft | 144 sq ft |
| Bedroom 2 | 11' × 10' | 42 ft | 2 / 1 | 279 sq ft | 110 sq ft |
| Bathroom | 8' × 5' | 26 ft | 1 / 1 | 172 sq ft | 40 sq ft |
| Hall | 10' × 3' 6" | 27 ft | 4 / 0 | 132 sq ft | 35 sq ft |
| Total | 247 ft | 1,619 sq ft | 673 sq ft |
Two coats on everything:
| Surface | Area × 2 coats | At 350 sq ft/gal | At 400 sq ft/gal | Buy |
|---|---|---|---|---|
| Walls | 3,238 sq ft | 9.3 gal | 8.1 gal | 10 gal (two 5-gal pails) |
| Ceilings | 1,346 sq ft | 3.8 gal | 3.4 gal | 4 gal |
If the walls and ceilings are new drywall, add one coat of primer over all 2,292 sq ft: at 200–300 sq ft per gallon that's 7.6–11.5 gallons, so 8–12 gallons depending on the product. Trim and doors come on top.
Quarts or gallons?
A gallon is 4 quarts. Quarts suit trim, doors, touch-ups and small bathrooms; walls call for gallons, and whole houses for 5-gallon pails. Quarts usually cost more per ounce. When the math lands just over a whole gallon, a quart might cover the rest, but coverage figures are approximate, so rounding up is safer. Leftover paint from the same batch is handy for touch-ups.
Doing it from the floor plan in FloorFigures
With a floor plan, you don't need to measure each wall. Open the plan in FloorFigures (free, in your browser) and find the rooms. Set a room's ceiling height and openings in its details, and the Takeoff tab shows each room's wall area less openings, ceiling area and paint gallons, using 350 sq ft per gallon and 2 coats unless you change them. Ceilings are included by default and can be left out. The same takeoff gives drywall sheets (see how many sheets of drywall), and a full material takeoff shows how it fits together.
Questions
- How much paint do I need for a 12x12 room?
- With 8 ft ceilings, a 12x12 room has 48 ft of wall × 8 ft = 384 sq ft. Take off a door (about 21 sq ft) and a window (about 15 sq ft) and you have 348 sq ft. Two coats at 350 sq ft per gallon is 1.99 gallons, so buy 2 gallons for the walls, plus 1 gallon if you're also painting the 144 sq ft ceiling.
- How many square feet does a gallon of paint cover?
- Sherwin-Williams says a gallon typically covers about 350–400 square feet, and a gallon of primer 200–300 square feet. Behr lists 250–400 square feet for its Premium Plus Interior Flat. Plan on 350 per gallon, per coat, and use less for rough or porous surfaces.
- How do I calculate wall square footage minus doors and windows?
- Add up the wall lengths to get the perimeter, multiply by the ceiling height, then subtract each door and window (width × height). A 3'0" × 6'8" door is exactly 20 sq ft. If you only have counts, about 21 sq ft per door and 15 per window is a common allowance.
- How much paint do I need for the interior of a house?
- Work it out room by room: there's no reliable rule from the house's square footage, because wall area depends on the layout and ceiling height. In our example, a small house with six rooms and 8 ft ceilings has 1,619 sq ft of walls and 673 sq ft of ceilings. Two coats take about 10 gallons for the walls and 4 for the ceilings.
- Do I need primer?
- Prime new drywall, bare patches and stained areas, and consider it for a big color change. Primer covers less than paint: Sherwin-Williams gives 200–300 square feet per gallon, so one coat on 1,000 sq ft takes 3.3–5 gallons: buy 4 or 5.
- How much paint do I need for a ceiling?
- A flat ceiling has the same area as the floor: length × width. A 12x12 ceiling is 144 sq ft, so two coats at 350 sq ft per gallon is 0.82 gallons, or 1 gallon. Some paint calculators, including Benjamin Moore's, leave the ceiling out, so add it yourself.