Rolling Offset Calculator
ConstructionCalculate pipe fitting travel length, run length, and true offset for a rolling offset. Enter set, rise, and fitting angle for accurate pipefitting layout.
Travel Length
20.4
Run Length
14.42
True Offset
14.42
What is a Rolling Offset?
A Rolling Offset Calculator determines the travel length and run length needed to route pipe between two parallel runs that are offset both horizontally and vertically, using two equal-angle fittings. This layout — common in plumbing, HVAC, and industrial piping — lets a pipefitter route around a beam, duct, or other obstruction while also stepping the pipe up or down to a new elevation, all with a single pair of fittings.
Getting the travel length right the first time saves material and rework, since cutting a pipe section too short or too long means starting over. This calculator applies the same trigonometry pipefitters have traditionally solved with constant multiplier tables, working directly from the set (horizontal offset) and rise (vertical offset) measured at the job site. For other measurement-based construction planning, see the SAG Calculator for cable and wire spans.
How to use this Rolling Offset calculator
- Measure and enter the Set (Horizontal Offset) in inches — the horizontal distance between the two pipe centerlines.
- Measure and enter the Rise (Vertical Offset) in inches — the vertical distance between the two pipe centerlines.
- Select the Fitting Angle you plan to use — 22.5°, 45°, or 60° — matching the fittings you have on hand.
- Review the True Offset result to confirm your set and rise measurements combine as expected.
- Read the Travel Length result and cut your pipe section to that measurement, using Run Length to mark fitting centerlines on the layout.
Formula & Methodology
The calculator applies standard pipefitting trigonometry: True offset = √(Set² + Rise²) Travel length = True offset ÷ sin(Fitting Angle) Run length = True offset ÷ tan(Fitting Angle) Worked example: A rolling offset with a 12 in set, an 8 in rise, and 45-degree fittings: - True offset = √(12² + 8²) = √208 ≈ 14.42 in - Travel length = 14.42 ÷ sin(45°) = 14.42 ÷ 0.7071 ≈ 20.39 in - Run length = 14.42 ÷ tan(45°) = 14.42 ÷ 1.0 = 14.42 in The pipefitter would cut a 20.39 in section of pipe and position the second fitting 14.42 in along the original pipe run from the first fitting.
Frequently Asked Questions
A rolling offset is a pipe route that changes direction in two planes at once — both horizontally and vertically — connecting two parallel but non-aligned pipe runs using two equal-angle fittings. It's common where pipe has to route around an obstruction while also stepping up or down to a different elevation.
First find the true offset using the Pythagorean theorem: the square root of the set squared plus the rise squared. Then divide the true offset by the sine of the fitting angle to get travel length, and by the tangent of the fitting angle to get run length.
Travel length is the actual length of pipe measured along the diagonal path between the two fittings — this is the piece you cut and thread or weld. Run length is the horizontal distance the offset covers when measured along the original pipe's centerline direction, used for laying out fitting positions.
45-degree fittings are the most common choice for rolling offsets because they balance a manageable travel length with reasonable flow characteristics. 22.5-degree fittings produce a longer, gentler offset with less flow resistance, while 60-degree fittings create a tighter, shorter offset when space is limited.
True offset is the straight-line diagonal distance between the two pipe centerlines, combining both the horizontal set and vertical rise into a single measurement using the Pythagorean theorem. It's an intermediate value used to calculate both travel length and run length, not a measurement you cut pipe to directly.
Yes, a rolling offset by definition combines a horizontal set and a vertical rise simultaneously, which is exactly what this calculator's Set and Rise inputs represent. If you only need a simple offset in one plane, the same travel and run formulas still apply using that single dimension as the offset.
Set is the horizontal distance between the centerlines of the two parallel pipe runs, and rise is the vertical distance between them. Measure both directly at the job site using a level and tape measure, or from isometric drawings if working from an engineering plan.
Using two fittings of the same angle — both 45 degrees, for example — ensures the resulting pipe section runs parallel to the original two pipe centerlines after the offset. Mismatched angles would leave the final connection out of alignment with the receiving pipe.
Pipefitters traditionally use constant multipliers (1.4142 for 45 degrees, 2.6131 for 22.5 degrees, 1.1547 for 60 degrees) to shortcut the trigonometry by hand. This calculator applies the exact trigonometric formulas directly, giving the same result as the constant method without needing to memorize the constants.
Yes, the rolling offset geometry is the same regardless of pipe material — the calculator works from set, rise, and fitting angle alone, independent of pipe diameter or material. Material only affects fitting selection and installation method, not the travel and run length math.
Measure set and rise as precisely as possible, ideally to the nearest 1/8 in, since small measurement errors compound through the trigonometric calculation and can result in a misaligned final connection. Double-check measurements at the job site before cutting pipe to the calculated travel length.
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