How much paint do you need for a room?
The useful number is not floor area. It is paintable wall and ceiling area multiplied by coats and divided by real coverage.
Room formulaWall area = 2 × (length + width) × height. Subtract major openings, add the ceiling if needed, then account for coats and coverage.
Measure perimeter and height
A 12-by-10-foot room with 8-foot walls has a 44-foot perimeter and 352 sq ft of gross wall area. Floor area alone would be only 120 sq ft, which is why using it for wall paint gives the wrong answer.
Subtract openings carefully
A typical interior door is roughly 21 sq ft and a common window might be estimated near 15 sq ft for planning. Measure unusually large openings. Small openings are often left in the area because edge work, roller loading, and touchups consume paint.
Multiply by coats
Two finish coats require twice the covered area of one coat. Primer is normally calculated as a separate product with its own coverage. New drywall, repairs, stains, and strong color changes may need a specific primer system.
Use the can, not a universal promise
Coverage varies by product and surface. Enter the range printed on the selected paint, then plan conservatively for texture, porosity, application technique, and leftover touchup material.
- Keep wall, ceiling, trim, and door products separate.
- Round to available can sizes after calculating gallons.
- Confirm ventilation, preparation, and recoat time on the label.