Roofs and rafters
Roof pitch chart: pitch to degrees and slope factor
Roofers in the US and Canada talk in pitch, rise per 12 in of run; saws and some plans talk in degrees. This chart converts between them, with the slope factor you multiply by to get lengths along the roof.
Roof pitch to degrees chart
Angle = arctan(pitch ÷ 12). Slope factor = √(1 + (pitch ÷ 12)²). The last column is how much rafter you need for every foot of level run.
| Pitch | Angle | Slope factor | Rafter per foot of run |
|---|---|---|---|
| 1/12 | 4.8° | 1.003 | 1 ft 0 1/16 in |
| 2/12 | 9.5° | 1.014 | 1 ft 0 3/16 in |
| 3/12 | 14.0° | 1.031 | 1 ft 0 3/8 in |
| 4/12 | 18.4° | 1.054 | 1 ft 0 5/8 in |
| 5/12 | 22.6° | 1.083 | 1 ft 1 in |
| 6/12 | 26.6° | 1.118 | 1 ft 1 7/16 in |
| 7/12 | 30.3° | 1.158 | 1 ft 1 7/8 in |
| 8/12 | 33.7° | 1.202 | 1 ft 2 7/16 in |
| 9/12 | 36.9° | 1.250 | 1 ft 3 in |
| 10/12 | 39.8° | 1.302 | 1 ft 3 5/8 in |
| 11/12 | 42.5° | 1.357 | 1 ft 4 1/4 in |
| 12/12 | 45.0° | 1.414 | 1 ft 5 in |
How do you convert degrees to a roof pitch?
Pitch = 12 × tan(angle). Round to the nearest whole or half inch, since that is how pitch is usually given.
Example. A roof at 30°: 12 × tan(30°) = 6.93, so close to a 7/12 pitch. A 7/12 roof is 30.3°.
What do the common pitches mean?
- 4/12 (18.4°): a low pitch, often seen on ranch houses and porches.
- 6/12 (26.6°): rises 6 in for every foot of run.
- 8/12 (33.7°): a steeper roof; the rafter is 1.2 times its run.
- 12/12 (45°): rises as much as it runs.
How low can a shingle roof go?
Under the US International Residential Code, asphalt shingles go on slopes of 2/12 or more, and from 2/12 up to 4/12 they need a double layer of underlayment. Shingle makers and local codes may ask for more, so check both.
How do you use the slope factor?
Multiply any level distance by the slope factor to get the distance along the roof. A 12 ft run at 6/12 needs 12 × 1.118 = 13.42 ft of rafter; a 1,200 sq ft footprint at 6/12 has 1,200 × 1.118 = 1,341.6 sq ft of roof.
Roof pitch in Clad
Every roof tool in Clad shows the pitch angle and the slope factor next to its result, and the pitch gauge reads the slope of a roof or a rafter with the phone's motion sensor. Type the pitch as 6 or 6/12.