How this hip rafter estimate works
The calculator converts common horizontal run into a simplified diagonal hip run, then combines that run with roof rise to estimate the sloped hip rafter length.
Simplified geometry only
This is useful for early layout planning on square-corner hip roof geometry. It does not calculate jack rafters, irregular hips, backing angles, plumb cuts, seat cuts, or structural sizing.
When to use a framing plan
Use drawings, supplier layouts, or qualified framing guidance before cutting lumber. Roof framing depends on span, loads, lumber size, species, grade, connectors, and local code.
Simplified hip rafter length checks
Examples use square-corner simplified hip geometry with no overhang. Cut details, irregular hips, jack rafters, and structural sizing are separate.
| Common run | 4/12 pitch | 6/12 pitch | 8/12 pitch |
|---|---|---|---|
| 8 ft | 11.62 ft | 12 ft | 12.51 ft |
| 10 ft | 14.53 ft | 15 ft | 15.63 ft |
| 12 ft | 17.44 ft | 18 ft | 18.76 ft |
| 16 ft | 23.25 ft | 24 ft | 25.02 ft |
Common roof pitch checks
Pitch is rise per 12 inches of run. Use plans or safe measurements; do not climb onto unsafe roofs for calculator inputs.
| Pitch | Approx. angle | Area multiplier |
|---|---|---|
| 4/12 | 18.4 degrees | 1.054x footprint |
| 6/12 | 26.6 degrees | 1.118x footprint |
| 8/12 | 33.7 degrees | 1.202x footprint |
| 12/12 | 45 degrees | 1.414x footprint |
Before you calculate
- Use common horizontal run in feet; the calculator converts it to a simplified diagonal hip run.
- Enter pitch as inches of rise per 12 inches of run.
- Add overhang as horizontal projection before calculating the sloped length.
Common mistakes
- Using rafter length as if it were a structural span approval.
- Forgetting that jack rafters, backing cuts, plumb cuts, seat cuts, and field trimming are separate.
- Applying one rafter length to roof sections with different run, pitch, or overhang.
Formula
hip rafter length = sqrt(((run + overhang) * sqrt(2))^2 + ((run + overhang) * pitchRise / 12)^2)
Assumptions
- This is a simplified square-corner hip geometry estimate.
- It does not calculate jack rafters, plumb cuts, seat cuts, or structural sizing.
- Use plans or qualified framing guidance before cutting lumber.
Example
Estimated hip rafter length: 19.5 ft
How to use this calculator
- Enter common run in ft.
- Enter pitch rise in in per 12.
- Enter overhang in ft.
- Review the live estimate and compare it with the example result.
- Check the formula, assumptions, product labels, and site conditions before using the Calculate Hip Rafter Calculator result to plan materials.
Before you buy materials
- Use the result as a layout check before selecting lumber lengths.
- Verify rafter size, spacing, species, grade, load, and code requirements separately.
FAQ
What is the example calculate hip rafter ft result?
Use common run, pitch rise, overhang, then calculate the planning result. In the default example, the result is 19.5 ft.
How do I estimate hip rafter length?
Use a diagonal plan run for the hip, calculate rise from pitch, then use the right-triangle hypotenuse of diagonal run and rise.
Is a hip rafter longer than a common rafter?
Usually yes for the same run and pitch, because the hip rafter travels diagonally across the roof plan.
Does this calculate rafter cuts?
No. It estimates length only. Plumb cuts, seat cuts, backing cuts, and jack rafter layout are separate.
Can this size rafters structurally?
No. Structural sizing requires span, load, lumber, spacing, connections, and code checks.
Related calculators
This calculator is for planning estimates only. Verify final quantities with product labels, project conditions, and a qualified professional when accuracy matters.