Roofing Calculators
Roofing calculators for pitch, rafters and shingles, with the formulas shown. Measure the footprint on the ground, find the pitch, and these tools turn it into roof area, rafter lengths and the materials to order.
Calculators
- Roof Pitch Calculator – pitch, angle, slope percent and roof area
- Rafter Length Calculator – rafter length, overhang and birdsmouth
- Roofing Calculator – squares, shingle bundles, underlayment and drip edge
Related guides
- Live Load vs Dead Load – how roof and snow loads are added up
- Snow Load on a Deck – snow weight by type and depth
Pitch at a glance
| Pitch | Angle | Area factor | Typical use |
|---|---|---|---|
| 2/12 | 9.5° | 1.014 | Low slope: membrane roofing, not shingles |
| 4/12 | 18.4° | 1.054 | Lowest common pitch for standard shingles |
| 6/12 | 26.6° | 1.118 | Common on houses; walkable |
| 8/12 | 33.7° | 1.202 | Steeper; harder to walk |
| 12/12 | 45.0° | 1.414 | Steep; needs roof jacks or harness |
Roof area = footprint including overhangs × area factor. One square = 100 sq ft.
Engineer's note: asphalt shingles need a minimum slope of 2/12, and slopes from 2/12 up to 4/12 need double underlayment (IRC R905.2). Below 2/12, use a low-slope membrane. Before adding a second layer of shingles, check the framing: sagging between rafters means the roof is already working hard.
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Maintained by: Engr. Abdul Latif, civil and structural engineer. Every calculator here shows its formula and the code table it follows. For planning only; confirm with your local building department.