Roofing Calculator: Shingles & Rafters
Measure the footprint from the ground, pick the pitch, and the pitch factor turns flat area into true roof area. You get squares, shingle bundles and the accessories, plus the common-rafter length for that pitch.
How this calculator works
- Plan area = (length + 2 × overhang) × (width + 2 × overhang).
- Roof area = plan area × pitch factor, where pitch factor = √(12² + rise²) ÷ 12. This holds for gable and hip roofs alike when all planes share the same pitch.
- Squares = roof area × (1 + waste) ÷ 100. Standard three-tab and architectural shingles come 3 bundles per square.
- Common rafter = (half the building width + overhang) × pitch factor. Hip length = √(2 × (W/2)² + rise²).
Roofing questions
How many bundles of shingles do I need?
Three bundles per square (100 sq ft) for most asphalt shingles. Find the roof area, add 10–15% waste, divide by 100 and multiply by 3. A 2,000 sq ft roof with 10% waste is 22 squares, or 66 bundles.
How do I measure a roof from the ground?
Measure the building footprint, add the overhang on every side, and multiply by the pitch factor for your roof slope. You can find the pitch with a level and tape: measure the rise over 12 in of run on a rafter tail or gable rake.
What is a roofing square?
100 square feet of roof surface. Shingles, underlayment and labor are usually priced per square.
How long is a rafter for a 6/12 pitch?
Multiply the run by 1.118 (the 6/12 pitch factor). For a 28 ft wide house the run is 14 ft, so the rafter is about 15.65 ft before the overhang; with a 12 in overhang, about 16.77 ft, so buy 18 ft stock.
Do hip roofs need more shingles?
Not for the same footprint and pitch; the area is the same. They do need more ridge cap for the hips and more waste from the angled cuts, which is why 15% is suggested.