What Is a Hip Rafter Length Calculator?
A hip rafter runs diagonally from a building corner up to the ridge, forming the sloped edge where two roof planes meet on a hip roof. Because it travels across the corner at 45° in plan view while also climbing the roof's pitch, its length can't be read straight off a common-rafter table — it needs its own calculation. This calculator applies the same 3D Pythagorean geometry framers use with a framing square, so you get an exact cut length instead of an eyeballed estimate.
Enter the common rafter run (the horizontal distance from the wall plate to the ridge), the roof pitch, and the tail overhang, and the calculator returns the full hip rafter length along with the numbers you need to lay out the cut.
How to Read Your Results
Hip Rafter Length
This is the total board length to cut, from the seat cut at the wall plate to the ridge end, measured along the top edge of the rafter (before any dropping or backing adjustments a framer makes at the ridge and birdsmouth).
Horizontal Hip Run
The horizontal (plan-view) distance the hip travels. It's longer than the common rafter's run by a factor of √2 (about 1.414×) because the hip crosses the building corner diagonally.
Total Rise
The vertical rise from the wall plate to the ridge over the full run, including the overhang portion, calculated using the roof's pitch.
Hip Rafter Slope Angle
The actual slope angle of the hip board itself. It's always shallower than the common rafter's roof-pitch angle at the same pitch, because the hip covers more horizontal distance for the same total rise.
Real-World Example
Take a common rafter run of 12 feet, a 6:12 roof pitch, and a 12-inch tail overhang.
| Value | Result |
|---|---|
| Total run (incl. overhang) | 13.0 ft |
| Horizontal hip run | ≈18.4 ft |
| Total rise | 6.5 ft |
| Hip rafter length | ≈19.5 ft |
Notice the hip rafter (≈19.5 ft) is noticeably longer than a common rafter would be over the same 13-foot run at the same pitch (≈14.5 ft) — that extra length is entirely due to the diagonal path across the corner.
Tips for Framing Hip Roofs
- Order stock a bit long. Hip rafters are among the longest boards on a roof — check availability before you're mid-build.
- This formula assumes a square, symmetric hip (equal pitches on both intersecting roof planes and a true 45° corner).
- Side cuts, backing and dropping at the ridge and birdsmouth are separate layout steps this calculator does not compute — use it for length only.
- Double-check your pitch input. A pitch entered as "6" means 6 inches of rise per 12 inches of run (a 6:12 roof).
Related Calculators
Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team