Rafter Length Calculator
Find the common rafter line length, rise and overhang tail from a run (or full span) and a pitch.
Calculate
Results
Draft — press Calculate| Rise | 6 ft |
|---|---|
| Line to wall | 13.42 ft |
| Tail (overhang) | 1.12 ft |
| Total line to eave | 14.53 ft |
| Angle to horizontal | 26.57° |
A common rafter runs straight up the slope from the eave to the ridge. Enter the common horizontal run, or the full building span which the tool halves, plus the pitch and any overhang. The result is the theoretical line length measured along the top of the rafter, with the eave tail reported separately.
Run, rise and line length
The rise equals the run times the pitch ratio p. The line length to the wall is the run times √(1 + p²). The overhang adds a sloping tail of overhang × √(1 + p²), so the total line to the outer eave is the sum of the two. Rise is always calculated from the wall run, not from the overhang.
What this tool does not do
These are geometric line lengths and an angle to the horizontal. They are not finished cutting lengths. Plumb cuts, the seat (birdsmouth) cut and any deduction for ridge-board thickness depend on a construction model and your own layout, so they are intentionally left out rather than guessed. For diagonal corners use the hip rafter calculator, which has different geometry.
Frequently Asked Questions
Do I enter run or span?
Either. Enter the common horizontal run directly, or the full span and the tool uses half of it as the run for a symmetric roof.
Is the tail included in the line length?
The tail is reported separately and added to the line-to-wall for the total line to the outer eave, so you can see each part.