Gable Roof Calculator: Rafter Length, Area and Shingles (2026)
The gable is the simplest roof to measure. Two rectangles, one ridge — and a little Pythagoras.
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A gable roof is two identical sloped rectangles meeting at a ridge. That makes it the easiest roof to calculate by hand — and the cheapest to build and reroof.
The gable roof formula
- Run = half the building width (plus overhang)
- Rise = run × pitch ÷ 12
- Rafter length = √(run² + rise²)
- Roof area = 2 × rafter length × building length (plus overhangs)
- Squares = area ÷ 100, then add 10% waste
Example: a 40 × 28 ft house with 1 ft overhangs at 6/12. Run is 15 ft, rise is 7.5 ft, rafter is 16.77 ft. Area = 2 × 16.77 × 42 ≈ 1,409 sq ft — about 15.5 squares with waste, or 47 bundles.
Why gables cost less
- Fewer cuts and less waste than hip roofs
- No hip ridges or valleys to flash
- Easy attic ventilation through gable vents
In high-wind zones, gable ends need bracing. Ask your roofer about gable-end straps — they're cheap insurance.
Enter span, length and pitch to get rafter length, squares and bundles instantly.
Open the Gable Roof CalculatorFAQs
What pitch is best for a gable roof?
4/12 to 9/12 is most common. Steeper sheds snow and rain better but costs more to install.
How much does a gable roof cost?
Reroofing with architectural shingles runs about $5.50–$7.50 per sq ft in 2026.
Is this for framing or shingles?
Both. Rafter length is for framing; area, squares and bundles are for roofing.
Written by Javed Niamat
Javed Niamat is a home renovation cost analyst and the founder of RenoCalc Hub. He tracks US remodeling labor rates, material pricing and contractor bids across all 50 states, and builds the free calculators behind every guide on this site.
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