Roof Pitch Calculator
Calculate roof pitch (slope), rise, run, and rafter length.
Convert between degrees, ratio, and percentage for any roof project.
Roof pitch is a measure of how steep a roof is. It is expressed as the ratio of vertical rise to horizontal run, typically written as “X in 12” in the United States — meaning the roof rises X inches for every 12 horizontal inches (1 foot). In metric countries, pitch is expressed as degrees or as a percentage grade.
The Rise-Over-Run Ratio
The most common format in North America: a 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance. A 12/12 pitch is a 45-degree angle. A 4/12 pitch is the minimum recommended for asphalt shingles.
Converting Between Formats
- Pitch to degrees: Angle = arctan(Rise ÷ Run)
- Degrees to pitch: Rise = Run × tan(Angle)
- Pitch to percentage: Percentage = (Rise ÷ Run) × 100
Rafter Length Formula
For a simple gable roof: Rafter length = √(Rise² + Run²) + overhang
This is just the Pythagorean theorem. The rafter is the hypotenuse of a right triangle.
Common Roof Pitches
| Pitch (X/12) | Degrees | Description |
|---|---|---|
| 2/12 | 9.5° | Very low — flat-looking, metal or flat roof required |
| 4/12 | 18.4° | Low-slope minimum for asphalt shingles |
| 6/12 | 26.6° | Moderate slope — very common |
| 8/12 | 33.7° | Steep — good drainage, more attic space |
| 12/12 | 45° | Very steep — high attic, dramatic look |
Roofing Material Minimums
| Material | Minimum Pitch |
|---|---|
| Standing seam metal | 1/12 |
| Flat / TPO / EPDM | 0–¼/12 |
| Asphalt shingles | 2/12 (with underlayment) or 4/12 (standard) |
| Wood shakes | 4/12 |
| Clay/concrete tile | 4/12 |
| Slate | 4/12 |
Multiplier for Roof Area
Roof surface area is larger than the horizontal projection area. The multiplier is: Area multiplier = √((Rise/Run)² + 1)
For a 6/12 pitch, the multiplier is √(0.5² + 1) = 1.118 — so a 1,000 sq ft footprint has 1,118 sq ft of actual roof surface.