6/12 Roof Pitch, Rafter Length, and Shingle Bundles
A 6/12 gable, 24 ft wide and 40 ft long, with a 12 in overhang.
Formula SSC-2026.1
6.00 / 12 · 26.57°
Pitch angle
26.57°
Multiplier 1.1180
Common rafter
14 ft 5 9/16 in
Tail 1 ft 1 7/16 in
Cuts
26.57° plumb
63.43° seat
Roof area
1,215 ft²
12.15 squares
Shingle bundles
41
3 bundles per square + 10% waste
Sheathing / felt
42 sheets
4 underlayment rolls
Delivery weight
4,914 lb
2,229 kg · 70 lb bundles, 46 lb sheets, 28 lb rolls
Rise and run are scaled from the span, overhang, and pitch. The small triangle is the pitch ratio.
| Item | Net | Waste | Order | Unit price | Line total |
|---|---|---|---|---|---|
| Architectural shingle bundles | 12.15 squares | 10% | 41 bundles | USD | $1,722.00 |
| 4x8 CDX sheathing | 38.0 sheets | 10% | 42 sheets | USD | $1,176.00 |
| Underlayment rolls | 1,215 ft² | overlap allowance | 4 rolls | USD | $220.00 |
| Ridge cap bundles | 42.0 ft ridge | — | 2 bundles | 25 ft per bundle | — |
| Pitch | Degrees | Multiplier | Rafter | Squares | Bundles | Sheets |
|---|---|---|---|---|---|---|
| 4.0/12 | 18.43° | 1.054 | 13 ft 7 5/8 in | 11.46 | 38 | 40 |
| 6.0/12 | 26.57° | 1.118 | 14 ft 5 9/16 in | 12.15 | 41 | 42 |
| 8.0/12 | 33.69° | 1.202 | 15 ft 6 9/16 in | 13.06 | 44 | 45 |
| 12.0/12 | 45.00° | 1.414 | 18 ft 3 9/16 in | 15.37 | 51 | 53 |
Show the deterministic formula
Angle = arctan(rise ÷ 12). Multiplier = √(1 + (rise ÷ 12)²). Gable run = span ÷ 2 − ridge thickness ÷ 2. Rafter length = (run + horizontal overhang) × multiplier.
Plumb cut = pitch angle. Seat cut = 90° − pitch angle. Area uses both slopes on a gable and one slope on a shed, and it includes a rake overhang equal to the eave overhang.
Bundles = ceiling of squares × 3 × 1.10. Sheets = ceiling of area × 1.10 ÷ 32. Rolls use 360 ft² effective coverage. Delivery weight plans 70 lb per bundle, 46 lb per sheet, and 28 lb per roll, then the header converts that pound total at 1 lb = 0.45359237 kg.
Contractor sign-off
Project: 6/12 Roof Pitch, Rafter Length, and Shingle Bundles
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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.
Engineering notes
A 6/12 pitch is 26.57 degrees and the multiplier is the square root of 1.25, about 1.118. On a 24 ft span the run to the face of a 1.5 in ridge is just under 12 ft. The rafter length adds a 1 ft horizontal overhang. Shingle bundles are 3 per square plus 10 percent. Sheathing is 4x8 sheets at 32 square feet plus 10 percent. The area includes a rake overhang equal to the eave.
Code reference
IRC R802 covers conventional wood roof framing and R905 covers roof coverings. This page does not size the rafter for snow or wind.
Field questions
- What is the 6/12 multiplier?
- It is √(1 + (6/12)²), which is √1.25, or about 1.118. Multiply the horizontal run in feet by that number.
- Does the rafter length include the overhang?
- Yes. The tail is also listed alone. The body stops at the ridge face, after half the ridge thickness is removed from the run.
- How are bundles counted?
- Roofing squares equal area divided by 100. Bundles equal that quantity times 3, then times 1.10, rounded up.