What roof pitch means
Pitch is the rise of the roof, in inches, for every 12 inches it runs horizontally. A 6/12 roof climbs 6 in per foot — 26.57°, or a 50% grade. Roofers, building codes and shingle makers all work in x/12, while phone apps and angle finders read degrees; the calculator converts both ways and adds the two multipliers you need to order material.
Pitch, slope and angle
On a modern job site "pitch" and "slope" both mean rise over a 12-in run. Older carpentry books define pitch as rise over the full span instead, so a 6/12 slope is a "¼ pitch" and a 12/12 slope a "½ pitch" — if a plan gives a single fraction, that is what it means. Angle is the same slope in degrees: 12 × tan(angle) converts it back to x/12. Percent grade, used for low-slope and site work, is simply rise ÷ run × 100, so 6/12 is a 50% grade.
Pitch to degrees and multipliers
| Pitch | Angle | Slope multiplier | Hip/valley factor |
|---|---|---|---|
| 2/12 | 9.46° | 1.014 | 1.424 |
| 3/12 | 14.04° | 1.031 | 1.436 |
| 4/12 | 18.43° | 1.054 | 1.453 |
| 5/12 | 22.62° | 1.083 | 1.474 |
| 6/12 | 26.57° | 1.118 | 1.5 |
| 7/12 | 30.26° | 1.158 | 1.53 |
| 8/12 | 33.69° | 1.202 | 1.563 |
| 9/12 | 36.87° | 1.25 | 1.601 |
| 10/12 | 39.81° | 1.302 | 1.641 |
| 12/12 | 45° | 1.414 | 1.732 |
The slope multiplier is √(1 + (rise/12)²). Multiply the plan area of the roof — the footprint plus overhangs, as seen from above — by it to get the real surface you'll cover. The hip/valley factor, √(2 + (rise/12)²), does the same for hips and valleys: multiply half the building width by it. CertainTeed's applicator manual prints 1.524 for 7/12; the exact value is 1.530.
How to measure your pitch
You don't need to walk on the roof. Any of these works:
- Level and tape, in the attic: hold a level horizontally against the bottom edge of a rafter, mark 12 in from the end that touches, and measure straight up from the mark to the rafter. A 6-in reading is a 6/12 pitch.
- At the gable, from a ladder: do the same against the rake board or fascia at the end of the house. A longer level (24 in) and halving the result reduces error.
- Phone or angle finder: lay it on the shingles or a rafter, read the degrees, and enter them in Angle mode. 12 × tan(angle) gives the rise: 30° is 6.93/12.
Rafter length from the pitch
A common rafter covers the run — half the building width — plus the overhang, stretched by the slope multiplier. For a 28-ft-wide house at 6/12 with a 12-in overhang: (14 + 1) × 1.118 = 16.77 ft, or about 16' 9¼", measured along the top edge. Subtract half the ridge board's thickness and allow for the plumb cut at the top and the tail cut at the bottom when you lay out the stock, then buy the next standard length up (18 ft here). The ridge sits 14 × 6/12 = 7 ft above the top of the walls.
What each pitch allows
- Under 2/12: no shingles (IRC R905.2.2). Use a membrane, standing seam metal (¼/12 and up) or sealed lapped metal (½/12 and up).
- 2/12 to under 4/12: shingles only over two layers of underlayment; CertainTeed asks for self-adhered membrane over the entire deck. Lapped metal panels need sealant in the laps below 3/12.
- 4/12 to 7/12: the comfortable, walkable range. Single-layer underlayment and four nails per shingle.
- 8/12 and steeper: roofers charge roughly $50–100 more per square, and where an ice barrier is required it must reach at least 36 in up the slope.
- Over 21/12: six nails and four dabs of roof cement per shingle.
Common mistakes
- Measuring along the sloped roof instead of level — the run must be horizontal.
- Using the pitch multiplier on hips and valleys; they need the hip/valley factor.
- Applying the hip factor to the hip's diagonal in plan rather than to half the building width.
- Assuming every face has the same pitch — porches and additions often differ, so measure each one.
With the pitch in hand, the roofing calculator turns your footprint into squares, bundles and the full shingle order — for example a 30×40 house at 6/12. Going metal? Try the metal roofing calculator.