In the US, roof pitch is written as rise over a 12-inch run: a 6/12 roof climbs 6 inches for every foot it runs horizontally. Contractors, shingle labels and building codes use that format, while apps, plans and solar tools often ask for degrees or percent. This guide gives you the full chart, the formulas behind it and a worked example from pitch to rafter length and roofing squares.
Roof pitch chart: pitch to degrees and percent
The rafter factor is what you multiply the horizontal run (or the flat footprint area) by to get the sloped length (or area).
| Pitch | Angle | Percent slope | Rafter factor |
|---|---|---|---|
| 1/12 | 4.8° | 8.3 % | 1.003 |
| 2/12 | 9.5° | 16.7 % | 1.014 |
| 3/12 | 14.0° | 25.0 % | 1.031 |
| 4/12 | 18.4° | 33.3 % | 1.054 |
| 5/12 | 22.6° | 41.7 % | 1.083 |
| 6/12 | 26.6° | 50.0 % | 1.118 |
| 7/12 | 30.3° | 58.3 % | 1.158 |
| 8/12 | 33.7° | 66.7 % | 1.202 |
| 9/12 | 36.9° | 75.0 % | 1.250 |
| 10/12 | 39.8° | 83.3 % | 1.302 |
| 11/12 | 42.5° | 91.7 % | 1.357 |
| 12/12 | 45.0° | 100.0 % | 1.414 |
| 14/12 | 49.4° | 116.7 % | 1.537 |
| 16/12 | 53.1° | 133.3 % | 1.667 |
| 18/12 | 56.3° | 150.0 % | 1.803 |
| 20/12 | 59.0° | 166.7 % | 1.944 |
| 24/12 | 63.4° | 200.0 % | 2.236 |
Degrees to pitch and percent
Going the other way, for example when a plan, an app or a solar quote gives you the angle:
| Angle | Pitch (x/12) | Percent slope |
|---|---|---|
| 5° | 1.05/12 | 8.7 % |
| 10° | 2.12/12 | 17.6 % |
| 15° | 3.22/12 | 26.8 % |
| 20° | 4.37/12 | 36.4 % |
| 22.5° | 4.97/12 | 41.4 % |
| 25° | 5.60/12 | 46.6 % |
| 30° | 6.93/12 | 57.7 % |
| 35° | 8.40/12 | 70.0 % |
| 40° | 10.07/12 | 83.9 % |
| 45° | 12/12 | 100.0 % |
A 20 degree roof is therefore a little steeper than 4/12, roughly 4⅜ in 12. A 30 degree roof is just under 7/12.
The formulas
Angle = arctan(rise ÷ 12)
Percent slope = rise ÷ 12 × 100
Rise per foot = 12 × tan(angle)
Rafter factor = √(rise² + 12²) ÷ 12
A common mix-up: percent is not degrees. A 100 % slope is 45°, because the roof rises one foot for every foot of run. Doubling the degrees does not double the percent, which is why the chart above is not linear.
How to measure the pitch of your roof
- From the attic (safest): hold a level horizontally against the underside of a rafter, mark 12 inches along the level, and measure straight up from that mark to the rafter. That measurement is the rise: 7 inches means a 7/12 pitch.
- On a gable end: measure the total height from the top plate to the ridge and half the building width. Rise ÷ run × 12 gives the pitch. Example: 6 ft rise over a 12 ft run is 6/12.
- With a phone: most phones have a level or measure app that shows the angle. Lay the phone on a rafter or on the rake board and read the degrees, then convert with the table.
- From the plans: elevation drawings usually show the pitch as a small triangle with 12 on the horizontal leg.
Only go on the roof itself with proper fall protection. For most purposes the attic or gable-end method is accurate enough.
Worked example: from pitch to roofing squares
A simple gable house is 24 ft wide with a 6/12 roof and a footprint, including overhangs, of 1,800 sq ft.
- Run: half the width, 24 ÷ 2 = 12 ft.
- Rafter length: 12 ft × 1.118 = 13.4 ft, plus the overhang measured along the slope.
- Roof area: 1,800 sq ft × 1.118 = 2,012 sq ft.
- Roofing squares: one square is 100 sq ft, so about 20.1 squares. Add roughly 10 to 15 % for waste, hips, valleys and starter courses.
The same multiplication works for any pitch: footprint area × rafter factor = sloped area. Hips and valleys need extra material, so complex roofs need a more detailed takeoff.
What the pitch means for roofing materials
| Range | Typical name | What it means |
|---|---|---|
| Below 2/12 | Flat or low slope | Membrane roofing such as TPO, EPDM or modified bitumen. Asphalt shingles are not allowed. |
| 2/12 to under 4/12 | Low slope | Asphalt shingles are allowed under the IRC, but only with a double layer of underlayment. |
| 4/12 to 9/12 | Conventional | Most US homes. Standard shingle installation; still walkable for roofers. |
| Above 9/12 | Steep slope | Needs roof jacks and extra safety gear. Many roofers charge more somewhere above about 7/12 to 8/12. |
Metal roofing has its own limits: standing-seam panels can go very low, while lapped panels usually need a steeper pitch. The manufacturer's installation instructions and your local code are what count.
Frequently asked questions
What is the most common roof pitch?
For houses in the US, pitches between 4/12 and 9/12 are the most common, with 6/12 a typical middle value.
How many degrees is a 4/12 roof pitch?
About 18.4°, or a 33.3 % slope.
How do I convert degrees to percent?
Take the tangent of the angle and multiply by 100. For 20°: tan(20°) × 100 = 36.4 %.
Is a 12/12 roof a 45 degree roof?
Yes. The rise equals the run, so the angle is exactly 45° and the slope is 100 %.
Does pitch affect solar panels?
Yes. Panels produce most when the tilt is close to the site's latitude, but in practice most pitches between about 4/12 and 9/12 work well. Installers use the angle in degrees for their yield estimate.