Roof pitch is how many inches a roof rises for every 12 in it runs across. A 6/12 roof (said "6 in 12") climbs 6 in per foot, an angle of 26.6°. Asphalt shingles need at least 2/12, with a double layer of underlayment below 4/12, and OSHA's safety rules call any roof over 4/12 a steep roof.
Roof pitch chart
Pitch is written as the rise over a run of 12: 4/12, 6/12, 8/12. The chart gives the angle, the same slope as a percent grade, and the slope factor, which turns a flat measurement into the length along the roof. A 6/12 roof is 26.6° and 50% grade, and every foot of run is 1.118 ft of roof.
| Pitch | Angle | Grade | Slope factor | Rise over a 12 ft run |
|---|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 | 1 ft |
| 2/12 | 9.5° | 16.7% | 1.014 | 2 ft |
| 3/12 | 14.0° | 25% | 1.031 | 3 ft |
| 4/12 | 18.4° | 33.3% | 1.054 | 4 ft |
| 5/12 | 22.6° | 41.7% | 1.083 | 5 ft |
| 6/12 | 26.6° | 50% | 1.118 | 6 ft |
| 7/12 | 30.3° | 58.3% | 1.158 | 7 ft |
| 8/12 | 33.7° | 66.7% | 1.202 | 8 ft |
| 9/12 | 36.9° | 75% | 1.250 | 9 ft |
| 10/12 | 39.8° | 83.3% | 1.302 | 10 ft |
| 11/12 | 42.5° | 91.7% | 1.357 | 11 ft |
| 12/12 | 45° | 100% | 1.414 | 12 ft |
| 14/12 | 49.4° | 116.7% | 1.537 | 14 ft |
| 16/12 | 53.1° | 133.3% | 1.667 | 16 ft |
| 18/12 | 56.3° | 150% | 1.803 | 18 ft |
Our arithmetic: angle = arctan(rise ÷ 12); grade = rise ÷ 12; slope factor = √(12² + rise²) ÷ 12. Pitches over 12/12 are steeper than 45°.
Pitch, slope and angle
Strictly, "4/12" is the roof's slope: rise over run. Pitch, in the older carpenter's sense, is the rise divided by the whole span of the building, wall to wall. InterNACHI, the home inspectors' association, says the two "do not mean the same thing", and gives 4/12 as a 1/6 pitch and 8/12 as a 1/3 pitch (InterNACHI). A 12/12 roof is a 1/2 pitch, because a gable rises half its span.
In everyday use, and on most product labels, "pitch" means the rise over 12, and that is how this page uses it. If a plan says "1/4 pitch", it means 6/12. To turn an angle into a pitch, take 12 × tan(angle): 30° is 6.9/12, almost 7/12.
How to measure roof pitch
You need a level, a tape measure and a pencil. The safest place to measure is in the attic, on a rafter, so you don't have to climb onto the roof.
- Mark 12 in on the level. Measure 12 in from one end and draw a line.
- Hold it level against a rafter. Put the end of the level against the underside of a rafter and hold it level, bubble centered (InterNACHI).
- Measure up at the mark. Measure straight up from the 12 in mark to the rafter. That number is the rise: 6 in means a 6/12 roof.
- Or use the gable end. From outside, measure the gable's height from the top of the wall to the peak, and half the width of the building. Rise ÷ half-width × 12 gives the pitch, near enough to choose a row in the chart.
On the roof itself, shingles are too uneven to give a true reading; InterNACHI suggests resting the level on a 48 in level or a straight 2×4 first. A phone angle app works too: read the angle and use the chart above.
Measure two or three rafters. Old roofs sag, and additions are often framed at a different pitch from the main house.
Minimum roof pitch by roofing material
The International Residential Code sets the lowest slope each roof covering may go on. Below these, water backs up under the laps.
| Roof covering | Minimum pitch | IRC 2021 |
|---|---|---|
| Asphalt shingles | 2/12 (double underlayment from 2/12 to 4/12) | R905.2.2 |
| Clay and concrete tile | 2½/12 (double underlayment up to 4/12) | R905.3.2 |
| Metal roof shingles | 3/12 | R905.4.2 |
| Mineral-surfaced roll roofing | 1/12 | R905.5.2 |
| Slate | 4/12 | R905.6.2 |
| Wood shingles and shakes | 3/12 | R905.7.2, R905.8.2 |
| Metal panels, lapped seams | 3/12, or ½/12 with lap sealant | R905.10.2 |
| Metal panels, standing seam | ¼/12 | R905.10.2 |
| Built-up, modified bitumen, single-ply, liquid-applied | ¼/12, for drainage | R905.9 to R905.15 |
Source: 2021 IRC chapter 9, section R905. Coal-tar built-up roofs may go down to 1/8 in per foot. Check the maker's instructions too: InterNACHI notes that most asphalt shingles are applied in the standard way from 4/12 to 21/12, with special steps on lower roofs.
So a "flat" roof is never quite flat: the code still wants a ¼ in fall per foot for drainage. Under 2/12, shingles are out and a membrane or standing-seam metal roof goes on instead.
Low slope and steep roofs
For fall protection on the job, OSHA draws the line at 4/12. A low-slope roof is one "having a slope less than or equal to 4 in 12", and a steep roof one "having a slope greater than 4 in 12" (OSHA 1926.500(b)). On a steep roof with edges 6 ft or more above the ground, workers must be protected by guardrails with toeboards, safety nets or personal fall arrest systems (OSHA 1926.501(b)(11)); low-slope roofs allow warning lines and safety monitors as well. If you are working on a roof yourself, treat anything above 4/12 with the same respect.
Pitch and how much roof there is
A steeper roof covers the same footprint with more material. Multiply the flat area by the slope factor from the chart: a 1,500 sq ft footprint at 6/12 has 1,500 × 1.118 = 1,677 sq ft of roof before overhangs. The roofing calculator does this for gable and hip roofs and turns it into squares and bundles of shingles.
Rafters work the same way along their length: each foot of run takes 1.118 ft of rafter at 6/12. The rafter calculator adds the overhang, the birdsmouth and ridge cuts, and the boards to buy.
Questions people ask
What is a standard roof pitch?
There is no single standard. The code lets asphalt shingles go as low as 2/12, and roofs above 4/12 count as steep under OSHA's rules. Pick the pitch from the roof covering, the look and what the attic needs, then check it against the minimums above.
What does a 6/12 roof pitch mean?
The roof rises 6 in for every 12 in it runs across, or 6 ft over a 12 ft run. That is an angle of 26.6° and a 50% grade.
What is a 4/12 pitch in degrees?
18.4°. A 5/12 roof is 22.6°, 7/12 is 30.3° and 8/12 is 33.7°.
Is a 3/12 roof too flat for shingles?
No, but it needs a double layer of underlayment, which the IRC requires for asphalt shingles from 2/12 up to 4/12 (R905.2.2). Below 2/12, use a membrane or metal roof instead.
How do I convert degrees to roof pitch?
Multiply 12 by the tangent of the angle. 20° gives 12 × 0.364 = 4.4, so about 4½/12; 45° gives 12/12.
What is the difference between 4/12 and 4:12?
None: both mean 4 in of rise per 12 in of run. You may also see it written as "4 in 12".
Sources
- International Code Council, 2021 International Residential Code, chapter 9: R905.2.2, R905.3.2, R905.4.2, R905.5.2, R905.6.2, R905.7.2, R905.8.2, R905.9.1, R905.10.2, R905.11.1, R905.12.1, R905.13.1, R905.15.1
- Occupational Safety and Health Administration, 29 CFR 1926.500 (definitions of low-slope and steep roofs) and 1926.501(b)(10) and (b)(11)
- InterNACHI, Measuring roof slope and pitch
Checked October 10, 2026. Angles, grades and slope factors are our arithmetic from the rise and run.