The short answer
Roof pitch is the rise in inches for every 12 inches of horizontal run. Divide the rise by the run and multiply by 12. A roof that rises 6 inches over 12 inches is a 6/12 pitch, which is an angle of 26.57°, a 50% slope and a roof-area multiplier of 1.118. To convert pitch to degrees, take the arctangent of rise ÷ run.
Pitch, angle and slope
- Pitch = rise per 12 units of run, written as x/12
- Angle = arctan(rise ÷ run), in degrees
- Slope % = rise ÷ run × 100
- Multiplier = √(1 + (rise ÷ run)²): multiply a footprint area by this to get the true roof area
- Rafter length per 12 of run = √(12² + rise²)
Worked example
You measure a rise of 8 inches over 12 inches of run:
- Pitch: 8/12
- Angle: arctan(8 ÷ 12) = 33.69°
- Slope: 8 ÷ 12 × 100 = 66.7%
- Multiplier: √(1 + 0.444) = 1.202
Roof pitch chart
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 |
| 2/12 | 9.46° | 16.7% | 1.014 |
| 3/12 | 14.04° | 25.0% | 1.031 |
| 4/12 | 18.43° | 33.3% | 1.054 |
| 5/12 | 22.62° | 41.7% | 1.083 |
| 6/12 | 26.57° | 50.0% | 1.118 |
| 7/12 | 30.26° | 58.3% | 1.158 |
| 8/12 | 33.69° | 66.7% | 1.202 |
| 9/12 | 36.87° | 75.0% | 1.250 |
| 10/12 | 39.81° | 83.3% | 1.302 |
| 12/12 | 45.00° | 100% | 1.414 |
What your pitch means
- Below 2/12 (flat or low slope): needs a membrane roof such as TPO, EPDM or modified bitumen.
- 2/12 to 4/12: shingles allowed only with extra underlayment.
- 4/12 to 9/12: conventional slope. Most houses fall here, and it is walkable with care.
- Above 9/12: steep slope. Sheds water and snow quickly, but needs roof jacks and harnesses to work on safely.
Frequently asked questions
What is a 4/12 roof pitch in degrees?
A 4/12 pitch is 18.43°. It is a common low-to-moderate slope and the lower limit for installing asphalt shingles with standard underlayment.
What is the most common roof pitch?
Pitches between 4/12 and 9/12 are the most common on houses. 6/12 is a popular middle ground that sheds water well and is still walkable.
What is the minimum pitch for shingles?
Asphalt shingles need at least a 2/12 pitch. Between 2/12 and 4/12, manufacturers require extra underlayment protection; below 2/12 you need a low-slope membrane roof.
How do I measure roof pitch from the ground?
Measure a gable end with a pitch gauge app on your phone, or measure inside the attic: put a level against a rafter, mark 12 inches along the level, and measure straight up to the underside of the rafter.
What is a 12/12 pitch?
A 12/12 pitch rises 12 inches for every 12 inches of run, a 45° angle and a 100% slope. It is considered steep and needs safety equipment to work on.
Sources
Related calculators
About this calculator. Every formula on this page is tested against worked examples from the sources above before publishing. Results are estimates for planning; confirm with your supplier or local code.
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