Roof Pitch Calculator: Convert Roof Pitch Between Rise/Run and Degrees
Convert between rise/run, pitch ratio, degrees, and percentage
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Rise-over-run slope
A 6cm/12cm pitch is 6/12 = 26.57° = 50%.
Roof pitch defines a roof's slope, typically as rise-over-run. In the US, '6/12' means 6 inches of vertical rise per 12 inches of horizontal run, converting to 26.6° or 50% slope. Standard residential pitches range from 4/12 to 9/12; anything below 2/12 requires specialized waterproofing materials, not standard shingles.
This Roof Pitch Calculator offers comprehensive conversions for all standard roof pitch formats: rise-over-run (e.g., 6/12), degrees, and percentage. It also accurately computes the total rafter length required for one side of your roof. Designed to align with International Residential Code (IRC) Chapter 9, the tool helps users understand if their roof falls into low-slope (under 2/12), standard residential (4-9/12), or steep-slope categories, guiding material selection and compliance. Essential for homeowners, contractors, and DIY enthusiasts, it simplifies complex roofing geometry, ensuring precise planning and material estimates for any project.
What is a roof pitch?
This roof pitch calculator provides comprehensive conversions between all four standard formats: rise-over-run (e.g., 6/12), decimal ratio, degrees, and percentage. Enter your roof's rise and run in inches, and the tool calculates the pitch in each format, alongside the crucial rafter length per side using the Pythagorean theorem. Designed in alignment with the International Residential Code (IRC) Chapter 9 roofing requirements and standard framing-square geometry, the calculator also features clear interpretation bands. These bands help users identify low-slope (under 2/12), standard residential (4–9/12), and steep (over 9/12) pitches, ensuring compliance and material suitability. It's an essential tool for homeowners, contractors, and DIY enthusiasts planning or assessing roofing projects.
The formula
- θ — pitch in degrees
- rise — vertical change (inches per 12 in run, conventionally)
- run — horizontal distance (12 inches in standard format)
Source: International Residential Code (IRC) Chapter 9 Roof Assemblies; standard framing-square geometry.
Worked examples
1Standard 6/12 residential pitch
Pitch ratio: 6/12 = 0.500. Angle: arctan(0.5) = 26.57°. Percent: 50%. Rafter length over 16 ft of horizontal span: √(16² + 8²) = √320 = 17.89 ft. Eaves typically add 1–2 ft of overhang, bringing the cut rafter to 18–19 ft. 6/12 is the most common modern US residential pitch — sheds snow well, allows attic space, and is easy to walk for installation.
2Low-slope 2/12
Pitch: 2/12 = 0.167 = 9.46° = 16.67%. Below the 4/12 minimum recommended for standard asphalt shingles, so this roof needs ice-and-water shield over the entire deck or a single-ply membrane. Rafter length over 20 ft of run: √(20² + 3.33²) = 20.28 ft. Low-slope roofs are easier to walk and shorter on materials but require more thoughtful drainage and waterproofing.
3Steep 12/12 (45°)
12/12 = 1.0 ratio = 45° exactly = 100% slope. Common in colonial-era and Tudor-style homes. Rafter length over 12 ft of run: √(12² + 12²) = 16.97 ft. Steep pitches shed snow and shed water rapidly but cost ~30% more in materials and require fall-protection harnesses for installation. The aesthetic is dramatic — and the attic space gained makes the upper level usable as living space.
How to use this calculator
- Rise (vertical) — How many inches the roof rises per 12 inches of horizontal run. Standard residential is 4–9; below 2 is 'low slope' and needs different roofing materials.
- Run (horizontal) — Horizontal distance. Construction industry standard is to express pitch over a 12-inch run.
- Total horizontal span (optional) — Half the building width — for one rafter run from ridge to outside wall. Used to compute total rafter length.
- Read the result. Use the worked examples below to sanity-check against a known scenario.
Common roof pitches with conversions
| Rise/Run | Decimal | Degrees | Percent |
|---|---|---|---|
| 1/12 | 0.0833 | 4.76° | 8.33% |
| 3/12 | 0.250 | 14.04° | 25.0% |
| 4/12 | 0.333 | 18.43° | 33.3% |
| 6/12 | 0.500 | 26.57° | 50.0% |
| 8/12 | 0.667 | 33.69° | 66.7% |
| 12/12 | 1.000 | 45.00° | 100.0% |
The 'pitch' name in some traditions also refers to the rise/span ratio (e.g. 'half pitch' = 12/12). Rise/run is the modern US convention.
Frequently asked questions
What's the standard residential roof pitch?
How do I measure my roof pitch?
How do I convert pitch to degrees?
What's the lowest pitch for asphalt shingles?
What's a 'flat' roof?
Why is pitch expressed over 12?
How does pitch affect roofing cost?
Does pitch affect attic space?
Roof Pitch glossary
How we built this calculator
Methodology
All four pitch expressions describe the same slope. The conversions:
This calculator was written by Numora team and reviewed by Numora engineering review team, Certified Building Inspector before publication. Both names link to full bios with verifiable credentials.
Sources & references
Every numeric assumption traces to a primary source.