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Rolling Offset Calculator — Pipefitting Trig
The layout math every fitter runs at the bender or the vise: enter the rise and the roll, pick your fitting angle, and get true offset, travel (center-to-center), and run.
Offset (rise)
Roll (blank = simple offset)
Fitting angle
The math behind a rolling offset
A simple offset moves pipe in one plane; a rolling offset moves it in two — up AND over at the same time. The trick is that both collapse to the same triangle once you find the true offset: the straight-line diagonal of the rise and the roll, true = √(offset² + roll²). It's the 3-4-5 triangle fitters already know — 3" up and 4" over is a 5" true offset.
From the true offset, the fitting angle does the rest. Travel — the center-to-center length of the diagonal piece — is true offset ÷ sin(angle). Run — how far the offset advances along the pipe axis — is true offset ÷ tan(angle). Shallower fittings need more travel for the same offset: a 22.5° offset takes more pipe than a 30°, which takes more than a 45°. At 60°, the run actually comes out shorter than the offset itself.
One thing this calculator deliberately does NOT do: subtract fitting takeouts. Travel is center-to-center; to cut pipe, subtract the takeout for each fitting on the diagonal. Takeouts vary by fitting size, type, and manufacturer, so they belong to your fitting tables, not a generic formula.
Worked example
A line needs to rise 3" and roll 4" using 45° fittings. True offset = √(3² + 4²) = 5". Travel = 5 ÷ sin 45° = 7.071" center-to-center, and run = 5 ÷ tan 45° = 5". Cut length = travel minus both fitting takeouts.
Frequently asked questions
What is a rolling offset in pipefitting?
An offset that changes the pipe's position in two planes at once — vertical rise and horizontal roll. Both combine into a single true offset, the diagonal √(rise² + roll²), which is then solved like a simple offset at your fitting angle.
What is the travel multiplier for 45 degree fittings?
1.414 (√2). Travel = true offset ÷ sin 45°, and 1/sin 45° = 1.4142 — so a 10" true offset needs 14.142" of travel center-to-center with 45° fittings.
Do I subtract fitting takeouts from the travel?
Yes. Travel is a center-to-center dimension. Subtract the takeout of each fitting on the diagonal to get the end-to-end cut length — takeouts depend on fitting size and type, so pull them from your fitting tables.
Which fitting angle uses the least pipe?
The steepest one. Travel = true offset ÷ sin(angle), so 60° fittings need the least travel and 22.5° the most for the same offset. The trade-off is that steeper fittings change direction more abruptly, which may not fit the rack.
Learn the code behind this calculator
Master the table, not just the answer
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