Pipe Offset Calculator (Simple and Rolling)
Simple and rolling pipe offsets: travel, run and the cut length between two fittings, for any fitting angle — with the constants and the cut-length rule from the US Army plumbing and pipe-fitting manual.
The method behind it: How to work out a pipe offset by hand — step by step, with sources.
Dimensions
Results
Preview
Sketch
Offset constants
| Fitting | Travel = offset × | Run = offset × |
|---|---|---|
| 11.25° | 5.1258 | 5.0273 |
| 22.5° | 2.6131 | 2.4142 |
| 30° | 2.0000 | 1.7321 |
| 45° | 1.4142 | 1.0000 |
| 60° | 1.1547 | 0.5774 |
How this tool is verified
- The travel constants match FM 3-34.471 Table 6-2 as printed for 60°, 45°, 30°, 22½° and 11¼°; the run constants agree except in the last digit — the manual truncates 0.5774 and 1.7321 to 0.5773 and 1.7320, and misprints 2.4142 and 5.0273 as 2.4140 and 5.0270; and the manual’s worked example (40 in at 45°: travel 56 9/16) is reproduced.
- Rolling offsets are checked independently by building the pipe as 3D vectors: the travel vector has the computed length and leaves the line at the fitting angle.
- Shop fractions are checked to round to the nearest 1/16 and reduce.
The method, the reports and the responsibility boundary are on the Verification page.
Built by Ruthen Systems
Free, with no account, and the dimensions you type never leave your browser. If a result looks wrong, or the option your shop needs is missing, say so — reports of a wrong result are dealt with first.
Report a problem or request a toolAssumptions and limits
Read these before you cut anything. They describe exactly what this tool does and does not account for.
- Both fittings have the same angle, and the pipe runs straight between them.
- Travel and run are centre-line dimensions. The cut length subtracts the fittings’ centre-to-end dimensions and adds the pipe’s engagement into each fitting, as the US Army plumbing manual sets out; take those dimensions from the actual fittings.
- A rolling offset is worked through its true offset, √(set² + roll²): the pipe still turns in one plane.
- Inch results are also shown to the nearest 1/16 in. Allow for weld gaps, thread make-up or solder sockets as your joint requires.
Output is a planning and fabrication aid. You are responsible for verifying dimensions, tolerances and material behaviour before production — full disclaimer.
Worked example
The US Army manual’s example: a 40 in offset in 3 in pipe with two 45° elbows of 4 5/8 in take-out and 1 in engagement.
- Travel56 9/16 in
- Cut length49 5/16 in
By hand: 40 × 1.4142 = 56.57; less 2 × 4 5/8 = 9.25; plus 2 × 1 = 2: 49.32 in.
Method
Sources
- FM 3-34.471, Plumbing, Pipe Fitting, and Sewerage (Headquarters, Department of the Army, 2001): offset constants, Table 6-2, p. 6-7; fitting dimension, para 6-17; offset and cut length, para 6-22, p. 6-6.
- Skilled Trades BC / TRU Open Press, BC Plumbing Apprenticeship Level 1, C-1.10 “Calculate Required Measurements for Piping Offsets” (CC BY-NC-SA 4.0): rolling offsets through the true offset.
Questions
What is the 45° offset multiplier?
1.4142 — the travel is the offset × 1.4142, and the run equals the offset. The general rule is travel = offset ÷ sin(angle) and run = offset ÷ tan(angle); the US Army plumbing manual FM 3-34.471 tabulates these constants (Table 6-2).
How do I work out a rolling offset?
Measure the set (how far up) and the roll (how far across). The true offset is √(set² + roll²) — the diagonal of that rectangle — and it goes through the same constants as a simple offset. Set 30 and roll 24 make a true offset of 38.42; with 45° fittings the travel is 54.33.
Why is my cut length shorter than the travel?
The travel runs from fitting centre to fitting centre. Each fitting takes up its centre-to-end dimension, and the pipe goes some way into each fitting. So the cut length is the travel, less both fittings’ dimensions, plus both engagements.
Where do I get the fitting take-out?
From the fitting itself or its maker’s data. It depends on the fitting type, size and standard, so the tool does not assume one; leave it at zero for centre-to-centre only.
Missing an option?
A different datum, an offset, a shop allowance, another shape altogether — say what this tool does not cover yet. Requests decide what gets built next, and a report of a wrong result is dealt with before anything new.
Rather have the whole part drawn — a shop drawing or a cut file from your sketch? That is paid drafting, quoted per job: drafting for small shops.
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