How the paint estimate is calculated
The room wall area is calculated from the room perimeter and ceiling height. A default area is deducted for each door and window. Ceiling area can be included, and the resulting paintable area is multiplied by the number of coats.
Wall area = 2 × (length + width) × height − openings
The required paint is the total coat area divided by the coverage you enter. The calculator rounds the purchase quantity up to whole gallons.