Calculate roof pitch angle in degrees, slope ratio, and rafter multiplier from rise and run. Used by roofing contractors, framers, and builders.
Rotary lasers and digital levels are the standard tools for verifying roof slope and layout. Shop roofing and framing tools at Express Tools.
Shop Express Tools →Roof pitch is expressed as rise over run — typically X/12 (rise in inches per 12 inches of horizontal run). A 6/12 pitch means 6 inches of rise for every 12 inches of run, equal to 26.57 degrees. Rafter length = horizontal run × rafter multiplier. For a 6/12 pitch, the multiplier is 1.118.
Roof pitch is the ratio of vertical rise to horizontal run, expressed in the standard X/12 format used throughout North American construction. The angle in degrees is calculated using the arctangent function:
The rafter multiplier is the most useful output for framers. Once you know the multiplier for your pitch, you can calculate any rafter run in seconds: just multiply by 1.118 (or whatever your pitch multiplier is). This avoids recalculating the hypotenuse every time. Multipliers are also used to calculate roof area — multiply the horizontal plan area by the pitch multiplier to get the actual sloped roof area, which is what determines shingle and underlayment quantities.
| Pitch | Degrees | Rafter Multiplier | Notes |
|---|---|---|---|
| 2/12 | 9.46° | 1.014 | Low slope — needs special shingles or membrane |
| 3/12 | 14.04° | 1.031 | Minimum for asphalt shingles on most codes |
| 4/12 | 18.43° | 1.054 | Common for garages, low-slope roofs |
| 5/12 | 22.62° | 1.083 | Common residential, sheds |
| 6/12 | 26.57° | 1.118 | Most common residential pitch |
| 7/12 | 30.26° | 1.158 | Fall protection required above this |
| 8/12 | 33.69° | 1.202 | Steep — good for attic space |
| 9/12 | 36.87° | 1.250 | High pitch, traditional styles |
| 10/12 | 39.81° | 1.302 | Very steep, dramatic appearance |
| 12/12 | 45.00° | 1.414 | Equal rise and run — 45 degrees exactly |
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Start free trialA 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. This equals 26.57 degrees — a moderate, common residential pitch.
Pitches up to 6/12 (26.6°) are generally walkable with caution. 7/12 and above require fall protection. Always use proper safety equipment on any roof.
Multiply the horizontal run of the rafter by the rafter multiplier to get the actual rafter length. For a 6/12 pitch, the multiplier is 1.118 — a 10-foot run needs an 11.18-foot rafter.
Enter rise (vertical inches) per run (horizontal inches, typically 12).