How do I convert degrees to roof pitch?
Multiply 12 by the tangent of the angle. A 26° roof has a rise of 12 × tan(26°) = 5.85 in per 12 in of run, so it is a 5.85/12 pitch, closest to 6/12. Roof pitch is always written as rise per 12 inches.
Degrees to roof pitch table
| Angle | Pitch | Closest whole pitch | Slope | Pitch factor |
|---|---|---|---|---|
| 5° | 1.05/12 | 1/12 | 8.7% | 1.004 |
| 10° | 2.12/12 | 2/12 | 17.6% | 1.015 |
| 15° | 3.22/12 | 3/12 | 26.8% | 1.035 |
| 20° | 4.37/12 | 4/12 | 36.4% | 1.064 |
| 25° | 5.6/12 | 6/12 | 46.6% | 1.103 |
| 30° | 6.93/12 | 7/12 | 57.7% | 1.155 |
| 35° | 8.4/12 | 8/12 | 70% | 1.221 |
| 40° | 10.07/12 | 10/12 | 83.9% | 1.305 |
| 45° | 12/12 | 12/12 | 100% | 1.414 |
| 50° | 14.3/12 | 14/12 | 119.2% | 1.556 |
| 60° | 20.78/12 | 21/12 | 173.2% | 2 |
Standard roof pitches fall between whole numbers of degrees. A 4/12 roof is 18.4°, 6/12 is 26.6°, 8/12 is 33.7° and 12/12 is exactly 45°.
Worked example: a 15° roof
- Find the tangent of the angle: tan(15°) = 0.268.
- Multiply by 12: 0.268 × 12 = 3.22 in of rise per 12 in of run.
- The roof is a 3.22/12 pitch, closest to 3/12.
- Slope: 0.268 × 100 = 26.8%.
- Pitch factor: √(1 + 0.268²) = 1.035, so the roof surface is about 3.5% larger than its footprint.
A 15° roof is a low slope. Under the International Residential Code, asphalt shingles need a slope of at least 2/12 and double underlayment below 4/12, so check the shingle maker’s instructions for roofs this shallow.
How the calculator works
Rise per 12 in = 12 × tan(angle)
Slope % = tan(angle) × 100
Pitch factor = √(1 + tan(angle)²)
To go the other way, from a measured rise and run to degrees, use the roof pitch calculator.
Frequently asked questions
What pitch is a 15 degree roof?
A 15° roof is a 3.22/12 pitch, closest to 3/12, with a slope of 26.8%.
What pitch is 26 degrees?
A 26° roof is a 5.85/12 pitch, closest to 6/12. An exact 6/12 roof is 26.57°.
What pitch is a 30 degree roof?
A 30° roof is a 6.93/12 pitch, closest to 7/12, with a slope of 57.7%.
What pitch is 45 degrees?
A 45° roof is a 12/12 pitch: it rises 12 inches for every 12 inches of run, a 100% slope.
Sources
- This Old House, How to Determine Roof Pitch
- International Code Council, 2021 International Residential Code, Chapter 9: Roof Assemblies