Gable area formula — ½ × width × peak height, with the peak height set by roof pitch
A gable is a triangle: area = ½ × width × peak height. The peak height comes from the pitch — (½ span) × pitch ÷ 12 — so a 30 ft wall at 6:12 is ½ × 30 × 7.5 = 112.5 ft².
What this diagram shows
A gable-end elevation showing how to find the area of the triangle above a wall. The gable is a triangle, so its area is one-half times the width times the peak height. The width is the span across the base, 30 feet. The peak height is the piece you cannot read off a tape: for a symmetric gable it comes from the roof pitch as half the span times the pitch divided by 12, so 15 feet times 6 over 12 equals 7.5 feet. A small inset defines the 6:12 pitch as 6 inches of rise per 12 inches of run. Putting it together, the gable area is one-half times 30 feet times 7.5 feet, which is 112.5 square feet.
Gable Area Calculator
Free gable area calculator: get the square footage of a gable end from width and roof pitch or peak height, plus rake trim length and siding waste.
