Gable Roof Calculator
Calculate total area, rafter length, ridge length, shingle quantity, and all key dimensions for a standard gable (A-frame) roof — just enter length, width, and pitch.
Gable Roof Dimensions
ft
ft
ft
ft
Total Roof Area
1,503 sq ft
Roofing Squares15.03 sq
Each Side751 sq ft
Footprint1,344 sq ft
Ridge Length42.0 ft
Rafter Length16.8 ft (+ 1.0 ft tail)
Gable Height7.5 ft
Each Gable End113 sq ft
Pitch Multiplier1.118×
Area Breakdown
Left slope751 sq ft
Right slope751 sq ft
Gable end #1113 sq ft
Gable end #2113 sq ft
Total roof area (slopes only)1,503 sq ft
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How to Use This Calculator
Enter your building dimensions and the calculator returns all the numbers you need:
- Building Length — The dimension parallel to the ridge (eave to eave along the long axis)
- Building Width — The dimension perpendicular to the ridge (this determines rafter run)
- Roof Pitch — Rise over 12 inches of run (e.g., 6/12)
- Overhang — How far the eaves extend beyond the wall (typically 12–24 inches)
Outputs include: total roof area, rafter length, ridge board length, number of roofing squares, shingle bundle count (with waste), and gable triangle area for siding estimates.
The Formula
Rafter Run = Building Width / 2
Pitch Multiplier = √(1 + (pitch/12)²)
Rafter Length = Rafter Run × Pitch Multiplier
Each Slope Area = Rafter Length × Building Length
Total Roof Area = Each Slope Area × 2
Ridge Length = Building Length
Gable Triangle Area = (Building Width / 2) × Ridge Height / 2
Ridge Height = Rafter Run × (pitch / 12)
Pitch Multiplier = √(1 + (pitch/12)²)
Rafter Length = Rafter Run × Pitch Multiplier
Each Slope Area = Rafter Length × Building Length
Total Roof Area = Each Slope Area × 2
Ridge Length = Building Length
Gable Triangle Area = (Building Width / 2) × Ridge Height / 2
Ridge Height = Rafter Run × (pitch / 12)
Example: 40 x 24 ft Gable Roof at 6/12
Example: 40 ft long, 24 ft wide house, 6/12 pitch, 18-inch overhang
Rafter Run24 / 2 = 12 ft
Pitch Multiplier1.118
Rafter Length (net)12 × 1.118 = 13.4 ft
Each Slope Area13.4 × 40 = 536 sq ft
Total Roof Area1,072 sq ft
Roofing Squares10.72 squares
Ridge Height12 × 0.5 = 6 ft
Gable Area (each end)24 × 6 / 2 = 72 sq ft
With 10% waste, order 12 squares (36 bundles) of architectural shingles. Total gable siding area is 144 sq ft (both ends combined).
Frequently Asked Questions
A gable roof has two sloping sides meeting at a central ridge, with triangular vertical ends called gables. It is the most common residential roof style in North America — simple to build, excellent at shedding water and snow, and good for attic space.
Measure the building footprint: length (parallel to ridge) and width (perpendicular). Measure or calculate your pitch. This calculator converts those three inputs into full roof dimensions — no ladder or measuring tape on the roof needed.
The most common residential pitch is 4/12–6/12. A 4/12 is walkable and economical. A 6/12 is attractive and very common in the South and Midwest. A 8/12+ looks dramatic but costs more to build and requires safety equipment during roofing work.
Gable triangle area = (Width × Ridge Height) / 2. Ridge height = Half-width × (pitch/12). For a 24 ft wide house at 6/12: height = 12 × 0.5 = 6 ft; area = (24 × 6) / 2 = 72 sq ft per gable end.
Gable roofs are more vulnerable to wind damage than hip roofs because the large vertical gable end creates wind pressure. In hurricane or high-wind zones, use hurricane straps, proper gable bracing, and consider a hip roof instead. Code requirements vary by wind zone.