In this guide
Which wall gets which color?
Make a plan view of the room and label the walls A, B, C, and D. Measure each wall's width and the height being painted. Record openings against the wall that contains them, then assign a product, sheen, and color to each remaining surface. This prevents a window from being subtracted twice or from the wrong paint color.
Example room: 14 by 11 feet with 8-foot walls. Wall A is the 14-foot accent wall, with a 4-by-5-foot window. Wall B is 11 feet wide with a 3-by-7-foot door. Wall C is 14 feet wide with no openings. Wall D is 11 feet wide with another 3-by-7-foot door. Use your measured opening sizes when filling in your own sheet.
The room has 338 square feet of wall surface
Multiply width by painted height for each gross area, then subtract only the openings assigned to that row. The four walls total 400 square feet. The window removes 20 square feet and the two doors remove 42, leaving 338 square feet of wall surface.
Wall A contributes 92 square feet to the accent color. Walls B, C, and D contribute 67 + 112 + 67 = 246 square feet to the main color. Check that 92 + 246 = 338. If that check fails, find the measurement or allocation error before adding paint allowances.
| Wall | Width × height | Openings | Net area | Finish group |
|---|---|---|---|---|
| A | 14 × 8 = 112 ft² | Window: 4 × 5 = 20 ft² | 92 ft² | Accent color |
| B | 11 × 8 = 88 ft² | Door: 3 × 7 = 21 ft² | 67 ft² | Main color |
| C | 14 × 8 = 112 ft² | None | 112 ft² | Main color |
| D | 11 × 8 = 88 ft² | Door: 3 × 7 = 21 ft² | 67 ft² | Main color |
| Total | 400 ft² | 62 ft² | 338 ft² | Two separate orders |
Which coverage range belongs in the sheet?
BEHR PREMIUM PLUS Interior Flat lists 250–400 square feet per gallon. BEHR PRO i300 Semi-Gloss lists 300–400, depending on texture, porosity, and application method, with spraying losses excluded. Enter the range for the product you are buying.
The table below uses the PREMIUM PLUS range of 250–400 square feet per gallon to show how coverage changes the purchase. Start with both ends of that range. A spray job also needs an allowance for application losses rather than relying on the published coverage alone.
Two coats plus a chosen reserve
For the main color, two coats cover 246 × 2 = 492 square feet of application. A chosen 10% reserve raises the quantity basis to 492 × 1.10 = 541.2 square feet. For the accent color, 92 × 2 × 1.10 = 202.4 square feet. Divide each figure by the relevant coverage to obtain gallons.
The example uses two coats and a 10% reserve. Check the required coat and primer schedule for your surface before ordering. If the old color still shows after the planned coats, another finish coat adds a full pass over the surface. Primer gets its own row and coverage figure.
Where the estimate crosses into another can
At 350 square feet per gallon, the main color needs 541.2 ÷ 350 = 1.5463 gallons and the accent color needs 202.4 ÷ 350 = 0.5783 gallon. A whole-one-gallon purchasing model therefore orders two main-color cans and one accent-color can.
At 250 square feet per gallon, the main-color estimate rises to 2.1648 gallons, requiring three whole cans, while the accent color still requires one. The same measured room now has a four-gallon two-color order instead of three. Round after applying coats and reserve, and round each paint group separately.
| Coverage per gallon | Main color: gallons / cans | Accent: gallons / cans | Total cans |
|---|---|---|---|
| 250 ft² | 2.165 / 3 | 0.810 / 1 | 4 |
| 300 ft² | 1.804 / 2 | 0.675 / 1 | 3 |
| 350 ft² | 1.546 / 2 | 0.578 / 1 | 3 |
| 400 ft² | 1.353 / 2 | 0.506 / 1 | 3 |
Why a second color can add a can
If all 338 square feet used one color at 250 square feet per gallon, two coats and the same reserve would require 338 × 2 × 1.10 ÷ 250 = 2.9744 gallons, or three whole cans. Dividing the room into two colors produces four whole cans at that coverage. The difference comes from rounding separate products, not from creating more wall area.
Check available package sizes and their prices. A quart-and-gallon combination may suit a fractional need, but do not reduce the reserve merely because a smaller package is convenient. If a third accent coat is needed, the accent estimate at 250 coverage becomes 92 × 3 × 1.10 ÷ 250 = 1.2144 gallons, crossing into a second one-gallon can.
Ceiling, trim, and doors need their own quantities
The 14-by-11-foot ceiling adds 154 square feet. At an assumed 350 square feet per gallon, two coats with 10% reserve require 154 × 2 × 1.10 ÷ 350 = 0.968 gallon: one gallon of ceiling paint. Pool that quantity with a wall estimate only when the product, sheen, color, and coat schedule are identical.
Measure paintable trim and door surfaces according to what will be coated. Subtracting a door opening from the wall does not estimate paint for the door itself. Likewise, returns, deep reveals, built-ins, or sloped areas need additional measured surfaces. Break an irregular wall into rectangles and triangles, label them, and avoid counting overlaps twice.
What to bring to the paint counter
Bring the area sheet, product name, sheen, color codes, coat count, and planned container sizes. Describe the existing finish and any bare or patched areas when asking about primer. Write the drying and recoat intervals beside the product so you can schedule the work as well as the purchase.
After the job, save the label details and note the quantity used. Record whether an extra coat or different preparation was needed. That makes the next estimate more informative than a note saying only that a room took two cans.