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From This Old House

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If you're painting walls it's important to use the door and window sections even if you're not painting the trim on them. The calculator will automatically subtract doors and windows from the wall area and reduce the wall paint you need accordingly.

Total length of walls in feet:

Round up to the nearest foot, and be sure to count all length. A room that's 12 x 15, for example, is 12 + 15 + 12 + 15 = 54 feet total in length.

Wall height in feet:

For rooms with knee walls, measure the room's height in two sections: from where the knee walls meet the floor to where they end, and from the top of the knee wall to where the pitched wall meets the ceiling. Add the two measurements for total wall height. Round up to the nearest foot. (Disregard the wall without a knee wall.)


This section will estimate the amount of paint you need to cover the doors and the door and window trim in a room, and will subtract the area of those openings from your wall measurements. The door section will assume you're painting a door and its surrounding trim. To calculate trim paint only (for example, for a doorway that doesn't have a door), include the doorway in your window trim section instead of in the door section.


Window height in inches:

Window width in inches:

Number of like-sized windows:

Round up to the nearest inch on these measurements.


Door height in inches:

Door width in inches:

Number of like-sized doors:

Round up to the nearest inch on these measurements.

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