Rafter length chart by roof pitch
The framing square's own numbers: inches of common rafter per foot of run, inches of hip per foot of common run, the slope in degrees, and the difference between one jack rafter and the next at 16" centres.
| Pitch | Common per foot of run | Hip per foot of run | Slope | Jack difference (16" oc) |
|---|---|---|---|---|
| 2:12 | 12 3/16" | 17 1/16" | 9.5° | 16 1/4" |
| 3:12 | 12 3/8" | 17 1/4" | 14.0° | 16 1/2" |
| 4:12 | 12 5/8" | 17 7/16" | 18.4° | 16 7/8" |
| 5:12 | 13" | 17 11/16" | 22.6° | 17 5/16" |
| 6:12 | 13 7/16" | 18" | 26.6° | 17 7/8" |
| 7:12 | 13 7/8" | 18 3/8" | 30.3° | 18 1/2" |
| 8:12 | 14 7/16" | 18 3/4" | 33.7° | 19 1/4" |
| 9:12 | 15" | 19 3/16" | 36.9° | 20" |
| 10:12 | 15 5/8" | 19 11/16" | 39.8° | 20 13/16" |
| 12:12 | 17" | 20 13/16" | 45.0° | 22 5/8" |
Reading it
- Multiply the common figure by the run in feet to get the line length, then add the tail.
- The hip figure is per foot of *common* run, not per foot of hip run — that is the convention stamped on a framing square.
- Asphalt shingles want at least 2/12, and below 4/12 they want doubled underlayment (IRC R905.2.2). Defaults, not law — ring the building department.
Sources: 2021 International Residential Code, International Code Council.
For the case this table does not cover
- Rafters
Common, hip and jack rafters for any pitch, with the birdsmouth laid out and the cut angles alongside.
- Roof truss calculator
Top chord, bottom chord and web lengths and angles for a king post, queen post or Fink truss — the geometry, not the engineering.
- Roofing calculator
Squares, bundles, starter strip, ridge cap and underlayment from a building footprint and a pitch.