A gable end is the classic ‘house shape’: a rectangle capped by a triangle. Side it accurately by measuring the two pieces separately and adding them. This guide shows the formula, the one measurement people get wrong, and how to convert area into squares of siding.
What’s in this guide
The gable wall area formula
Area = (width × wall height) + ½(width × rise)
Rectangle below the eave line plus the triangle above it.How to measure a gable end
- Measure the wall width at the eave line, in feet.
- Measure the wall height from the foundation to the eave (bottom of the triangle).
- Measure the rise straight up from the eave line to the ridge peak — the vertical height of the triangle, not the sloped rake length.
- Compute both areas: rectangle = width × wall height; triangle = ½ × width × rise.
- Add them and apply waste, then subtract large windows or doors.
Worked example: a gable end
| Part | Measurement | Area |
|---|---|---|
| Lower wall (rectangle) | 24 ft × 9 ft | 216 sq ft |
| Gable (triangle) | ½ × 24 ft × 6 ft | 72 sq ft |
| Wall total | — | 288 sq ft |
| + 10% waste | — | 29 sq ft |
| Order | — | 317 sq ft ≈ 3.2 squares |
!
Measure rise, not rake
The sloped edge (rake) is longer than the vertical rise. Using it inflates the triangle. Always use the straight-up height to the peak.
Siding coverage & waste
| Siding type | Sold as | Typical waste |
|---|---|---|
| Vinyl lap siding | Squares (100 sq ft) | 10% |
| Fiber-cement lap | Planks / squares | 10% |
| Board & batten | Boards | 12–15% |
| Cedar shingle / shake | Squares / bundles | 15% |
| Engineered wood panel | 4×8 or 4×9 sheets | 10% |
Common mistakes
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Doubling the triangle
The triangle is ½ base × height — not width × rise. Forgetting the ½ doubles the gable area.
i
Ignoring the second gable
Most houses have two gable ends. Measure and order for both if they're being sided.
✓
Steep roofs need more
A tall, steep gable has a big triangle and long rake cuts. Lean toward the higher waste figure.
Key takeaways
- Gable area = rectangle (W×H) + triangle (½ W×rise).
- Use the vertical rise to the peak, never the sloped rake.
- Siding sells in 100 sq ft squares; add 10–15% waste.
- Subtract large windows and doors; keep small ones in the total.
Related calculators & guides
Frequently asked questions
- How do I calculate the square footage of a gable wall?
- Add the rectangular lower wall (width × wall height) to the triangular gable (½ × width × rise to the peak). A 24 ft wide wall that is 9 ft to the eave with a 6 ft rise = 216 + 72 = 288 sq ft.
- What is the area of the triangle part of a gable?
- It is half the base times the height: ½ × wall width × the vertical rise from the eave line to the ridge. The two roof slopes do not matter for area — only the horizontal width and vertical rise.
- How much siding waste should I add for a gable wall?
- Add about 10% for lap siding and panels, and up to 15% for board-and-batten or shingle siding where every course meets the angled rake and needs cutting.
- Should I subtract windows and doors from siding?
- Subtract large openings such as picture windows and doors. Leave small windows in the total — the waste factor covers the trimming around them.