A rolling offset is the pipefitter’s classic puzzle: a pipe that must move sideways and up or down at once, connected by a diagonal piece running through three dimensions. This calculator solves it exactly, returning the true offset, the diagonal travel between fitting centers, and the cut length after fitting take-out.
How it works
The roll and rise form two legs of a right triangle whose hypotenuse is the true offset. The diagonal pipe travel then follows from the fitting angle:
true offset = √( roll² + rise² )
travel = true offset / sin(fitting angle)
run (along axis) = true offset / tan(fitting angle)
cut length = travel − (take-out of both fittings)For the common 45 degree fitting, sin(45°) and tan(45°) both simplify nicely: travel equals the true offset times 1.414, and the run equals the true offset. Shallower 22.5 degree fittings produce a longer travel of about 2.61 times the true offset.
Example and notes
Suppose a pipe must roll 8 inches sideways and rise 6 inches, using 45 degree fittings. The true offset is √(8² + 6²) = 10 inches. The diagonal travel is 10 / sin(45°) = 14.14 inches center to center. If each fitting has a 1.5-inch take-out, the actual pipe cut is 14.14 − 3.0 = 11.14 inches. Always confirm take-out from your fitting’s laying-length chart, because it varies by pipe size, material, and fitting angle.
Common fitting angles and their multipliers
Pipefitters memorise multipliers for the two most-common angles to avoid pulling out a calculator on the job:
| Fitting angle | Travel multiplier (× true offset) | Run multiplier (× true offset) |
|---|---|---|
| 45° | 1.414 | 1.000 |
| 22.5° | 2.613 | 2.414 |
| 11.25° | 5.126 | 5.027 |
| 60° | 1.155 | 0.577 |
For a 45° fitting the travel is simply the true offset times 1.414 — easy to do in your head once you know it. The 22.5° multiplier of 2.613 means the pipe must travel more than twice as far along the diagonal, which needs more clearance but improves flow.
What is fitting take-out and why it matters
Take-out (also called make-up, thread engagement, or center-to-face distance) is the amount of the fitting’s length that a pipe enters when it is joined. For threaded fittings, it is the depth of thread engagement; for butt-weld fittings, it is zero because the pipe butts to the fitting end; for socket-weld and solvent-weld, it is the socket depth.
If you cut the pipe to the center-to-center travel and forget to subtract take-out, the assembled offset will be shorter than planned and the pipe will not reach its destination. The cut length is always:
cut = travel − take-out₁ − take-out₂Take-out values are listed in each fitting manufacturer’s dimension tables and vary by pipe material (PVC, CPVC, copper, carbon steel, stainless) and nominal size. Always look them up rather than guessing.
Simple vs rolling offsets
A simple offset moves in one plane only — either purely horizontal or purely vertical. Its geometry collapses to the basic two-triangle case without needing the three-dimensional true-offset step.
A rolling offset moves in both planes simultaneously. The pipe’s path spirals through space, which is why you need the true offset (the 3D hypotenuse) before applying the fitting-angle multiplier. Treat any run where the pipe changes both elevation and side-to-side position as a rolling offset rather than two separate simple offsets — doing two separate simple offsets in sequence introduces an extra bend and extra fittings.
Checking your work on site
After marking the pipe at the computed cut length, double-check by dry-fitting the offset with both elbows but without gluing or tightening. The assembled piece should sit flat in space — no twist, no forced angle — and align with both the source and destination pipe stubs within your allowable tolerance. If it does not line up, measure the actual roll and rise again; a measurement error of even an inch can throw off the cut by several inches on long offsets.