How to calculate roof pitch
The slope of a roof is the vertical rise in inches for every horizontal 12 inches of run, and it is written with the rise first: a 4 inch rise for every horizontal foot is a 4 in 12 slope, or 4:12. [3] From the rise, the other numbers follow: angle = atan(rise / 12), slope percent = rise / 12 x 100, and pitch multiplier = the square root of (1 + (rise / 12) x (rise / 12)). Give the calculator any one of the rise, the angle or the slope percent, and it fills in the other two.
Worked example
A 6/12 roof rises 6 in for every 12 in of run. The angle is atan(6 / 12) = 26.57 degrees. The slope is 6 / 12 x 100 = 50 percent. The pitch multiplier is the square root of (1 + (6 / 12) x (6 / 12)) = 1.1180. Over a run of 12 in, the sloped side is 13.42 in long (12 x 1.1180). For a 12 ft run, the rafter is 13.4164 ft.
How to measure roof pitch
A fairly easy way is to use a 12 inch carpenter's level. Set one end on the roof surface and level it. Then use a tape measure or a ruler to measure from the other end of the level down to the roof surface. That number of inches is the rise in 12. Free smartphone applications with a slope indicator may also help. [3]
What is the roof pitch multiplier?
The pitch multiplier turns the flat area under a roof into the roof area, and a run into the length of the sloped side, which is the rafter. For 6/12 it is 1.1180. A 1,200 square foot footprint has a roof of 1,341.64 square feet. The roofing calculator does this sum for you and counts the squares and bundles. To turn a run in feet into the sloped side in feet, multiply by the same number: the rise and the run are both over 12 inches, and 12 inches make a foot, so the multiplier does not change with the unit. [2]
Roof pitch chart: pitch in degrees and percent
Every whole pitch from 1/12 to 12/12, with its angle in degrees, its slope percent and its pitch multiplier.
| Pitch | Angle (degrees) | Slope (%) | Multiplier |
|---|---|---|---|
| 1/12 | 4.76 | 8.33 | 1.0035 |
| 2/12 | 9.46 | 16.67 | 1.0138 |
| 3/12 | 14.04 | 25.00 | 1.0308 |
| 4/12 | 18.43 | 33.33 | 1.0541 |
| 5/12 | 22.62 | 41.67 | 1.0833 |
| 6/12 | 26.57 | 50.00 | 1.1180 |
| 7/12 | 30.26 | 58.33 | 1.1577 |
| 8/12 | 33.69 | 66.67 | 1.2019 |
| 9/12 | 36.87 | 75.00 | 1.2500 |
| 10/12 | 39.81 | 83.33 | 1.3017 |
| 11/12 | 42.51 | 91.67 | 1.3566 |
| 12/12 | 45.00 | 100.00 | 1.4142 |
What is a 4/12 pitch roof?
A 4/12 roof rises 4 inches for every 12 inches of run. That is 18.43 degrees, or 33.33 percent, with a multiplier of 1.0541. OSHA's fall protection rules call a roof low-slope when its slope is less than or equal to 4 in 12. [1]
What is a 5/12 pitch roof?
A 5/12 roof rises 5 inches for every 12 inches of run. That is 22.62 degrees, or 41.67 percent, with a multiplier of 1.0833.
Roof pitch in degrees
To go from degrees to a pitch, choose Angle in the calculator, or read the table. The rise is 12 x tan(angle).
| Angle (degrees) | Rise in 12 (in) | Slope (%) |
|---|---|---|
| 5 | 1.05 | 8.75 |
| 10 | 2.12 | 17.63 |
| 15 | 3.22 | 26.79 |
| 20 | 4.37 | 36.40 |
| 25 | 5.60 | 46.63 |
| 30 | 6.93 | 57.74 |
| 35 | 8.40 | 70.02 |
| 40 | 10.07 | 83.91 |
| 45 | 12.00 | 100.00 |
What is the minimum roof pitch for shingles?
The Asphalt Roofing Manufacturers Association says asphalt shingles are intended for roof decks having a slope of no less than 2 inches per foot (2:12). It says never to apply shingles on slopes lower than 2:12. Most asphalt shingles may be installed on roof slopes from 4:12 to 21:12 using standard application methods, and most may be used on slopes from 2:12 to less than 4:12 if special low slope application procedures are followed. [3] A 2/12 roof is in that lower range. Follow the shingle maker's instructions.
Roof pitch by roof type
The slope of a roof is determined in part by its style. The manual illustrates shed, gable, mansard, gambrel and hip roofs. [3] We found no source that gives one standard pitch for each style, so this page does not. What limits the pitch is the roof covering:
| Covering | Lowest slope |
|---|---|
| Asphalt shingles (special procedures below 4:12) | 2:12 |
| Roll roofing, exposed nail method (generally) | 2:12 |
| Roll roofing, concealed nail method (generally) | 1:12 |
Source: the Asphalt Roofing Manufacturers Association manual. [3]
What are common roof pitches?
We found no source that ranks pitches by how common they are, so this page does not name a standard one. The chart above lists every whole pitch from 1/12 to 12/12. The manual says most asphalt shingles may be installed on roof slopes from 4:12 to 21:12 using standard application methods. [3]
What does roof pitch change?
A steeper pitch makes a larger roof for the same footprint, so it needs more material: see the multiplier above. This tool covers only the geometry. Ask your building authority about loads and framing.
Common mistakes and limits
- Mixing up percent and degrees. A 50 percent slope is 26.57 degrees, not 50.
- Measuring over a run that is not 12 inches. The slope is written as the rise over 12 inches of run. [3]
- Using the multiplier on the wrong area. Multiply the flat footprint, not the roof area you have already measured on the slope.
- Treating OSHA's low-slope line as a building code. It is a definition in the fall protection rules. [1]
- What this tool does not cover: overhangs, birdsmouth cuts, ridge boards, loads and framing.
Frequently asked questions
What is my roof pitch?
Set one end of a 12 inch carpenter's level on the roof surface and level it. Then use a tape measure or a ruler to measure from the other end of the level down to the roof surface. That number of inches is the rise in 12, so 6 inches is a 6/12 pitch. [3]
What is the difference between roof pitch, slope and angle?
ARMA writes the slope with the rise first, over a run of 12 inches, such as 4 in 12 (4:12). ARMA's glossary defines pitch as the rise over the whole span, which is half the slope; this page uses 6/12 the way roofers write the slope, as the rise in 12 inches of run. [3] The angle is the steepness in degrees from flat, and the slope percent is the rise divided by the run times 100. A 6/12 roof is 26.57 degrees, or 50 percent.
Does roof pitch change the roof area?
Yes. A pitched roof is larger than the flat area under it. Multiply the flat area by the pitch multiplier: for 6/12 it is 1.1180, so a 1,200 square foot footprint has a roof of 1,341.64 square feet. The roofing calculator does this for you.
Is a 4/12 roof low-slope?
OSHA's fall protection rules call a roof low-slope when its slope is less than or equal to 4 in 12, so a 4/12 roof is low-slope by that definition. The Asphalt Roofing Manufacturers Association uses a different line for shingles: it treats slopes from 4:12 up as standard, and slopes below 4:12 as low slope. [1][3]
Sources and references
- Occupational Safety and Health Administration (OSHA). 29 CFR 1926.500, Fall protection: scope, application and definitions (accessed November 2026). Used for: The definitions of a low-slope roof and a steep roof.
- National Institute of Standards and Technology (NIST). NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (SP 811, accessed November 2026). Used for: the inch and foot relationship (12 inches in a foot).
- Asphalt Roofing Manufacturers Association (ARMA). Residential Asphalt Roofing Manual (2014 edition, accessed November 2026). Used for: how slope is written as rise over a 12 inch run, the lowest slope for shingles and roll roofing, the 4:12 to 21:12 range for standard methods, the special low slope procedures, the roof styles it illustrates and the 12 inch level method of measuring slope.
How we use sources: methodology.
Estimates only. Confirm quantities with your supplier. See the disclaimer. Found a wrong result? Report an error.