You only need a tape measure and four numbers: the room's length, width, ceiling height, and how many doors and windows it has.
Measure the length of each wall at floor level and add them together. For a rectangular room, that's 2 × (length + width). Multiply by the ceiling height to get the total wall area.
You don't paint doors and windows, so take them out. Use about 21 sq ft per door and 15 sq ft per window, or measure yours for a closer number.
Plan on two coats. One coat is only enough when you're repainting the same color over walls in good shape.
Check the label. Most interior paints say 350 to 400 sq ft per gallon. Textured walls, bare drywall and dark-to-light color changes use more, so plan on 250 to 300 sq ft per gallon for those.
| Perimeter | 2 × (14 + 16) = 60 ft |
| Wall area | 60 × 9 = 540 sq ft |
| Minus 2 doors, 3 windows | 540 − 42 − 45 = 453 sq ft |
| Two coats | 906 sq ft |
| Divide by 350 | 2.6 gallons |
| Buy | 3 gallons |
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If you need 4 gallons or more of the same color, a 5-gallon bucket usually costs less than four single gallons and keeps the color consistent across walls.
Use primer on new drywall, patched areas, stains, or when going from a dark color to a light one. Primer coverage is similar to paint, so you can use the same math for one coat.
Interior paint · Roller kit · Painter's tape · Drop cloth
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