Roof Pitch Calculator
Roof pitch tells you how steep a roof is, and framers, roofers, and material suppliers all need it in slightly different formats. Enter your rise and run and this calculator converts between pitch, slope percentage, angle, and rafter length in one pass.
Measure rise and run over the same section of roof — e.g. the total rise and run from the ridge to the eave. The calculator converts this to a standard “X/12” pitch.
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Details
Pitch is expressed as rise per 12 in of run, so divide your total rise (in inches) by your total run (in feet) to get the X in X/12. Slope percentage is that same ratio expressed as a percent (rise/run × 100). The roof angle in degrees is the arctangent of rise over run. Rafter length per foot of horizontal run comes from the Pythagorean theorem: the square root of (run² + rise²) using 12 in of run as the base unit.
Common Roof Pitches
Here’s how common X/12 pitches translate to angle and slope percentage. Use this to sanity-check your own numbers or compare against a design you’re quoting.
| Pitch (X/12) | Angle | Slope % |
|---|---|---|
| 3/12 | 14.04° | 25% |
| 4/12 | 18.43° | 33.3% |
| 6/12 | 26.57° | 50% |
| 8/12 | 33.69° | 66.7% |
| 12/12 | 45° | 100% |
How to Calculate Roof Pitch
- Measure rise the vertical height gain, in inches, using a level and tape measure along the roof.
- Measure run the horizontal distance covered, in feet, over that same section.
- Divide rise by run and multiply by 12 to get the X/12 pitch.
- Convert to angle take the arctangent of rise over run for the roof angle in degrees.
- Find rafter length use the Pythagorean theorem to get rafter length per foot of run.
Worked example
A rise of 72 in over a run of 12 ft works out to a common 6/12 pitch.
- Rise72 in
- Run12 ft
- Pitch6/12
- Slope50%
- Angle26.57°
- Rafter length per ft of run13.416 in
Pitch and Material Choice
Pitch determines what roofing materials you can legally and practically install. Most asphalt shingles need at least a 2/12 pitch with special low-slope underlayment, and 4/12 or steeper for standard installation. Standing seam metal and low-slope membranes (TPO, EPDM) can go as low as 1/4:12. A 6/12 pitch like the example above is a conventional, walkable roof that works with nearly every material on the market, which is part of why it’s such a common default in residential framing.
Common mistakes
- Measuring rise off-levelrise has to be measured straight up from a level line, not along the sloped roof surface, or the ratio comes out wrong.
- Confusing pitch with anglea 6/12 pitch is 26.57 degrees, not 6 degrees or 12 degrees. They’re related but not interchangeable numbers.
- Using the wrong run unitpitch is rise per 12 inches of run, so mixing feet and inches without converting throws off every downstream number.
- Skipping the overhangrafter length from this calculator covers the run you entered only; add eave overhang separately when ordering rafter stock.
What this calculator assumes
Adjust your result if your project differs from these.
- Rise and run are measured accurately with a level, not along the sloped surface.
- Calculations assume a simple straight-slope roof (no hips, valleys, or curved sections).
- Rafter length is the theoretical run-to-ridge measurement and does not include eave overhang or ridge board thickness.
- Pitch is expressed in the standard X/12 convention used in US residential framing.
Common questions
What does a 6/12 roof pitch mean?
It means the roof rises 6 inches for every 12 inches (1 ft) of horizontal run. That works out to a 26.57 degree angle and a 50% slope.
How do I measure rise and run on an existing roof?
Hold a level horizontally against the roof surface for exactly 12 in of run, then measure straight down to the roof from the end of the level to get rise.
What's the difference between pitch and slope percentage?
Pitch is rise per 12 in of run (like 6/12). Slope percentage is the same ratio multiplied by 100, so 6/12 pitch equals 50% slope.
Do steeper roofs need more material?
Yes. Steeper pitches have more actual surface area than the flat footprint suggests, and rafter length increases with pitch, so shingle and rafter counts both go up.
What's the minimum pitch for asphalt shingles?
Most manufacturers require at least 2/12 with double underlayment, and 4/12 or steeper for a standard shingle warranty. Check your specific product’s install guide.
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Roof Pitch Calculator Result
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Result
| Rise | — |
| Run | — |
| Pitch | — |
| Slope percent | — |
| Angle | — |
| Rafter length | — |
Notes
Estimate generated by materialcalculate.com.