How to measure exterior paintable area — wall rectangle plus gable triangle, minus the big openings
Measure a gabled wall in two pieces: the rectangle (width × wall height) plus the gable triangle (½ × width × rise), then subtract the large openings. Net area ÷ coverage × coats = gallons. Add every wall and gable for the whole house.
What this diagram shows
A gable-end house elevation broken into the pieces of a paint take-off. The wall is a rectangle equal to its width times its wall height, and the gable above the eave line is a triangle equal to one-half its width times its rise. Add the rectangle and the triangle, then subtract the large openings such as the garage door and entry door; small windows are usually left in because you still paint the trim around them. The net paintable area divided by the surface coverage and multiplied by the number of coats gives the gallons needed. Add every wall and every gable to get the whole-house area.
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