What is a gable roof?

A gable roof is the most common roof style in North America. It has two sloping sides that meet at a central ridge, with triangular gable ends on each side. Also called a peaked or A-frame roof, it is simple to build, provides good attic space, and sheds rain and snow effectively.

How do I calculate the area of a gable roof?

Gable Roof Area = (Building Width / 2) × Pitch Multiplier × 2 × Ridge Length. Or more simply: Footprint Area × Pitch Multiplier. A 40×30 ft house with 6/12 pitch: footprint = 1,200 sq ft × 1.118 = 1,342 sq ft total roof area.

How much does it cost to build a gable roof?

Framing a new gable roof costs approximately $4–$8 per square foot of roof area for labor and lumber. Adding roofing materials (shingles, underlayment, etc.) brings total cost to $8–$18 per sq ft. A 1,500 sq ft gable roof might cost $12,000–$27,000 to frame and shingle.

What are the advantages of a gable roof?

Gable roofs are cost-effective (simple framing), excellent at shedding water and snow, provide good attic ventilation via gable vents, and allow for attic living space. They are also the easiest roof type for DIY construction.

What is the difference between a gable and hip roof?

A gable roof has two sloping sides and two vertical triangle ends (gables). A hip roof slopes down on all four sides with no vertical ends. Hip roofs are more resistant to wind damage, but cost more to build and provide less attic space. Gable roofs are simpler and less expensive.

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

Building Length (ft)?

Building Width (ft)?

Roof Pitch?

Eave Overhang (ft)?

Rake Overhang (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

Link copied to clipboard

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)

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.

Related Calculators

Sources & References

The formulas, code requirements, and reference data used in this calculator are sourced from the following authoritative organizations and publications. Local codes vary — always verify with your jurisdiction's building department.

International Residential Code (IRC) 2024 — Chapter 9: Roof Assemblies — ICC
NRCA Roofing Manual (Steep-Slope & Low-Slope) — National Roofing Contractors Association
Asphalt Shingle Installation Manual — ARMA (Asphalt Roofing Manufacturers Association)
GAF Roof Measurement Guide — GAF
NRCA Project Pricing Guidelines — NRCA

Disclaimer: Calculator results are estimates intended for planning and educational purposes only. They do not replace professional engineering analysis, building permit review, or contractor estimates. Always consult a licensed roofing contractor or structural engineer for final specifications.