True offset first, then travel
A rolling offset moves in two directions at once, so the real distance the pipe has to cover is the diagonal of the rise and the set. Find that true offset, then divide by the sine of the fitting angle to get the center-to-center travel between the two fittings.
The angle sets the multiplier
Once you have the true offset, the fitting angle fixes how much longer the travel is. Divide by the sine of the angle, or just multiply by the constant below.
| Fitting angle | sin(angle) | Travel = true offset × |
|---|---|---|
| 22.5° | 0.3827 | 2.6131 |
| 45° | 0.7071 | 1.4142 |
| 60° | 0.8660 | 1.1547 |
45° is the shop standard: an easy 1.4142 factor and the most common elbow on the shelf. A 22.5° run is gentler on flow but needs far more pipe.
Getting it right on the job
- Offset is not travel. The offset is how far the line shifts; travel is the diagonal pipe length that actually spans it. Cutting the pipe to the offset leaves it short.
- Measure center to center. The formula gives the distance between the two fitting centers. Subtract each fitting's take-out (the length it eats up) to get the pipe you actually cut.
- Roll and set are separate. The rise is the vertical change and the set is the horizontal shift. Combine them into the true offset before touching the travel formula.
Common questions
What is a rolling offset in piping?
It is a run that shifts both sideways and up or down at the same time, so the pipe travels diagonally through three dimensions. You size it from the true offset, which combines the vertical rise and the horizontal set into one distance.
What is the travel formula for a 45-degree rolling offset?
First find the true offset with the Pythagorean theorem: true offset equals the square root of rise squared plus set squared. Then travel equals true offset divided by the sine of the fitting angle. For 45-degree fittings the sine is 0.7071, so travel is true offset times 1.4142.
Why is 45 degrees the standard fitting angle?
A 45-degree elbow gives a clean 1.4142 multiplier and is the most stocked fitting. Shallower angles like 22.5 degrees stretch the run out and need more pipe, but they ease flow and reduce pressure loss.
