Rolling Offset Calculator - Travel, Run and True Offset for Pipe Fittings
Calculate true offset, centerline travel, run, and roll angle for pipe rolling offsets using set, roll, and fitting angle. Built for plumbers, pipefitters, and HVAC techs laying out 45, 30, 22.5, and 60 degree offsets. Pair with our pipe weight calculator to check load and hanger spacing on the finished run.
🔧 Rolling Offset Calculator
Set & Roll → True Offset → Travel & Run | 45°, 30°, 22.5°, 60° Fittings
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Rebar Weight Chart
US Standard Rebar Sizes (#2–#18) with weight per foot, diameter, and cross-sectional area.
View Chart →Fitting Angle Multiplier Lookup
These are the standard pipefitter constants used to convert true offset into travel and run. Multiply the true offset by the number in the table to get each dimension without a calculator [1][2].
| Fitting Angle | Travel Multiplier (÷ sin) | Run Multiplier (÷ tan) |
|---|---|---|
| 60° | 1.1547 | 0.5774 |
| 45° | 1.4142 | 1.0000 |
| 30° | 2.0000 | 1.7321 |
| 22.5° | 2.6131 | 2.4142 |
At 45°, run equals the true offset exactly, which is why many field pipefitters use that angle as a mental shortcut when laying out standard offsets [3].
What Makes an Offset "Rolling"
A standard offset moves a pipe sideways in a single plane, like shifting left or right around an obstruction. A rolling offset moves the pipe in two planes simultaneously, combining a horizontal shift (set) with a vertical shift (roll) between the same two fittings.
Because the pipe changes direction diagonally through 3D space, you cannot use the set or roll directly to size the fittings. Instead, the true offset combines both measurements using the Pythagorean theorem: true offset equals the square root of set squared plus roll squared [4].
From True Offset to Travel and Run
Once true offset is known, the layout becomes a standard offset problem. Travel, the actual pipe length between fitting centerlines, equals true offset divided by the sine of the fitting angle. Run, sometimes called setback or advance, equals true offset divided by the tangent of the fitting angle [1][2].
For 45 degree fittings this simplifies to familiar numbers: travel equals true offset times 1.4142 (the square root of 2), and run equals true offset times 1.0000, meaning run equals true offset exactly at this angle [3].
Why the Roll Angle Matters
The roll angle, found as the arctangent of roll divided by set, tells you how far to rotate the pipe when marking your fitting layout lines. Skipping this step is one of the most common reasons a rolling offset fitting lands rotated incorrectly, even when the travel length is right. For related structural framing checks around pipe penetrations, see the beam load calculator.
Field Scenario: Routing Around a Duct
🔧 Scenario: 8 in Set, 6 in Roll, 45° Fittings
Set = 8 in, Roll = 6 in, Fitting = 45°
Travel = 10 × 1.4142 = 14.14 in.
Run = 10 × 1.0000 = 10.00 in.
Roll angle = arctan(6/8) = 36.87°.
A 5-3/4 in exact match to a standard 90 degree duct penetration; the pipefitter marks the 36.87° roll angle on the pipe before laying out the two 45° cuts.
🔧 Scenario: Adding Fitting Take-Off
Travel = 14.14 in, Take-off per fitting = 0.75 in (two fittings)
Travel measures centerline to centerline. The actual pipe stock cut is always shorter once both fitting take-offs are subtracted.
⚠ Common Error: Using Run Instead of Travel
Pipefitter cuts pipe to the 10 in run value instead of the 14.14 in travel value
Run tells you how far the offset advances along the original line. Travel tells you the actual diagonal pipe length. Cutting to run on anything but a 90 degree offset produces a pipe that is too short.
Mistakes That Waste Pipe on Rolling Offsets
⚠ Confusing Set and Roll with True Offset
Set and roll are independent measurements in different planes. Neither one alone tells you the fitting size or cut length. Only the combined true offset, found via the Pythagorean theorem, is usable for layout [4].
💡 Forgetting to Subtract Fitting Take-Off
Travel is a centerline measurement. Always subtract the take-off of both fittings from travel to get the true cut length of pipe stock, per standard pipefitting practice [4].
⚠ Applying the 45° Constant to a Different Angle
The 1.4142 travel multiplier only applies to 45 degree fittings. Using it for 22.5 or 60 degree fittings produces incorrect travel and run values; each angle has its own sine and tangent multiplier [1][2].
💡 Skipping the Roll Angle Mark
Even with correct travel and run, a rolling offset fitting installed without marking the correct roll angle will land rotated, misaligning the final connection point.
Frequently Asked Questions
A rolling offset happens when a pipe changes direction in two planes at once, shifting sideways (set) and vertically (roll) between two points. The true offset is the diagonal distance combining both movements, found with the Pythagorean theorem: true offset equals the square root of set squared plus roll squared.
Travel equals the true offset divided by the sine of the fitting angle. For a 45 degree fitting, sine of 45 degrees equals 0.7071, so travel equals true offset multiplied by 1.4142.
For 22.5 degree fittings, the travel multiplier is 2.6131 (1 divided by sine of 22.5 degrees) and the run multiplier is 2.4142 (1 divided by tangent of 22.5 degrees), based on standard pipefitter trigonometric tables.
Travel is the actual diagonal length of pipe between the centerlines of the two fittings. Run, also called setback or advance, is the horizontal distance the pipe advances along its original line of direction.
Travel measures center-to-center distance between fittings, not the physical pipe you cut. Each fitting has a take-off dimension, the distance from its centerline to where the pipe actually seats, and both take-offs must be subtracted from travel to get the correct cut length.
Roll angle equals the arctangent of rise divided by set, giving the angle at which the true offset diagonal sits relative to the horizontal set direction. This angle is used to mark the correct rotational orientation on the pipe before cutting.
The trigonometry is identical for round pipe used in plumbing, gas piping, and HVAC refrigerant lines, since all rolling offsets rely on the same set, roll, and fitting-angle relationship regardless of the specific trade.
Sources and Methodology
Last reviewed: July 2026.
- [1] Standard pipefitter trigonometric offset formulas: travel = true offset ÷ sin(angle); run = true offset ÷ tan(angle), as documented in TheBuildingCode.com, Pipe Offset Calculator.
- [2] Fitting angle multiplier tables for 22.5°, 45°, and 60° fittings, as summarized in Reference.com, How Do You Calculate Pipe Offset.
- [3] 45 degree constant (1.4142 travel multiplier) confirmed across multiple pipefitting trade references and field practice, including plumbing trade forums and instructional trade video content.
- [4] True offset via Pythagorean theorem (offset = √(set² + roll²)) and fitting take-off subtraction methodology, consistent with standard journeyman and master plumber trade math instruction.
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