Estimates only. Check measurements, product labels and local building codes before you buy or build.
How the Parallel Offset Calculator works
When several pipes run side by side and all make the same offset, starting every offset at the same point would pinch them together through the angled section. This calculator tells you how much further along each next pipe has to start so the center-to-center spacing stays the same all the way through, plus the travel and run that every pipe shares.
Each next pipe starts further along the run by spacing × tan(A ÷ 2), where A is the fitting angle and the spacing is center to center. tan(A ÷ 2) is the spread constant on fitter charts: 22½° 0.199, 30° 0.268, 45° 0.414, 60° 0.577. Pipe 2 starts one advance after pipe 1, pipe 3 two advances, and so on. The travel and run are those of a simple offset: offset ÷ sin A and offset ÷ tan A.
Example: three pipes 12" apart making a 24" offset with 45s. Advance = 12 × 0.414 = 4.97", 5" to the nearest 1/16". Pipe 1 starts at 0, pipe 2 at 5" and pipe 3 at 2 × 4.97 = 9.94" (9 15/16"). Every pipe has a travel of 24 × 1.414 = 33.94" (33 15/16") and a run of 24".
Number the pipes from the one on the inside of the first bend: it starts first, and each pipe further out starts one advance later. Measure every start mark from pipe 1's mark rather than from the one before it, so rounding does not add up. The spacing is measured square to the runs.
Multiply the center-to-center spacing by tan(half the fitting angle) and start each next pipe's offset that much further along the run. For 45s that is spacing × 0.414: pipes 12" apart start 4.97" (5") apart.
What is the spread multiplier for 45 degree parallel offsets?
0.414, which is tan 22½°. For other fitting angles: 22½° 0.199, 30° 0.268, 60° 0.577. Multiply it by the spacing between the pipes.
Do all pipes in a parallel offset have the same travel?
Yes. Every pipe makes the same offset with the same fittings, so the travel and run are identical; only the start mark moves. In the three-pipe example every travel is 33 15/16".
Which pipe starts first in a parallel offset?
The pipe on the inside of the first bend. Each pipe further out starts one advance later, because it has further to go around the turn.