Roof Angle Calculator
Convert rise and run to roof angle in degrees, pitch ratio, and slope percentage.
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What Is Roof Pitch and Why Does It Matter?
Roof pitch — or slope — describes how steeply your roof rises for every 12 inches of horizontal run. A 4/12 pitch means the roof rises 4 inches for every 12 inches across. The angle in degrees is the arctangent of that ratio.
Pitch affects material costs, labor rates, water drainage speed, and even which roofing materials are approved for your roof type. Flat roofs require specialized waterproof membranes; very steep roofs need safety equipment and take longer to install.
Common Roof Pitches and Their Angles
| Pitch Ratio | Angle (degrees) | Slope % | Category |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | Low slope |
| 3/12 | 14.04° | 25% | Low slope |
| 4/12 | 18.43° | 33.3% | Moderate |
| 6/12 | 26.57° | 50% | Moderate steep |
| 8/12 | 33.69° | 66.7% | Steep |
| 12/12 | 45.00° | 100% | Very steep |
How to Measure Roof Pitch
The easiest way: hold a level horizontally against the roof, measure 12 inches along the level from where it meets the roof, then measure vertically down to the roof surface. That vertical measurement is your rise — giving you a X/12 pitch ratio.
Pitch Factor for Material Estimates
The pitch factor tells you how much larger the actual roof surface is compared to the building footprint. A 6/12 pitch has a pitch factor of √((6/12)² + 1) = 1.118 — meaning the roof is 11.8% larger than the floor plan suggests.
Minimum Pitch Requirements by Material
- TPO / EPDM flat roofing: 0.25/12 minimum
- 3-Tab asphalt shingles: 2/12 minimum
- Architectural shingles: 4/12 recommended
- Metal panel: 3/12 minimum (depends on seam type)
- Tile: 4/12 minimum, 6/12+ recommended
- Wood shake: 4/12 minimum
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