4/12 roof pitch in degrees and slope
A 4/12 pitch is 18.43° from level, a 33.3% grade and a 1:3 ratio. The rafter multiplier, √(1 + (4/12)²) = 1.0541, turns level run into rafter length and plan area into roof area.
4/12, 6/12, 8/12 and 12/12 compared
| Pitch | Degrees | Slope | Rafter multiplier | Rafter per ft of run | Hip per ft of run |
|---|---|---|---|---|---|
| 4/12 | 18.43° | 33.3% | 1.0541 | 12.65 in | 17.44 in |
| 6/12 | 26.57° | 50% | 1.118 | 13.42 in | 18 in |
| 8/12 | 33.69° | 66.7% | 1.2019 | 14.42 in | 18.76 in |
| 12/12 | 45° | 100% | 1.4142 | 16.97 in | 20.78 in |
- 6/12 roof pitch: 26.57°, rises 6 in per foot; a common house pitch.
- 8/12 roof pitch: 33.69°; steeper roofs shed snow faster but need more roof area per footprint.
- 12/12 roof pitch: 45°, rise equals run; the rafter multiplier is 1.414.
What roofing works on a 4/12 roof?
Every covering in the IRC list is allowed at 4/12. It is above the 2/12 minimum for asphalt shingles and the 2-1/2/12 minimum for clay or concrete tile, and it is exactly where both stop needing double underlayment. It also meets the 3/12 minimum for metal and wood shingles and the 4/12 minimum for slate[1].
| Covering | Minimum pitch | At 4/12 |
|---|---|---|
| Asphalt shingles | 2/12 | allowed |
| Clay or concrete tile | 2.5/12 | allowed |
| Metal roof shingles | 3/12 | allowed |
| Wood shingles or shakes | 3/12 | allowed |
| Slate | 4/12 | allowed |
| Mineral-surfaced roll roofing | 1/12 | allowed |
| Standing-seam metal panels | 0.25/12 | allowed |
| Lapped metal panels, no sealant | 3/12 | allowed |
| Lapped metal panels with sealant | 0.5/12 | allowed |
| Built-up, modified bitumen, single-ply | 0.25/12 | allowed |
Framing a 4/12 roof
At 4/12 a 24 ft wide gable rises 4′ 0″ to the ridge line, which leaves a low attic. Ridges, hips and valleys need beam design only below 3/12[2]. Size the rafters with the rafter calculator, count squares with the roof calculator and convert any other pitch with the roof pitch calculator.
Frequently asked questions
What angle is a 4/12 roof pitch?
18.43 degrees.
Is a 4/12 roof pitch good for shingles?
Yes. Asphalt shingles are allowed from 2/12, and at 4/12 and above the IRC no longer requires double underlayment.
What is a 6/12 roof pitch in degrees?
26.57 degrees, a 50% slope.
What is the multiplier for a 12/12 roof?
1.414 (the square root of 2): every foot of run needs 16.97 in of rafter.
What angle is an 8/12 roof pitch?
33.69 degrees, a 66.7% slope with a rafter multiplier of 1.202.
What is a 12/12 roof pitch?
A 45° roof that rises 12 in for every 12 in of run, a 100% slope; its rafters are 1.414 times the run.