How the Rolling Offset Calculator works
A rolling offset moves a pipe up or down (the rise) and sideways (the roll) at the same time with one pair of fittings, so the angled piece runs on a diagonal. This calculator turns rise and roll into the true offset, then gives the travel, the run and how far to roll the fittings off vertical. When the run is fixed instead (both ends already set), the Run known mode finds the fitting angle you need.
Look along the pipe: rise and roll are the two legs of a right triangle, and its diagonal is the true offset, T = √(rise² + roll²). From there it works like a simple offset: travel = T ÷ sin A and run = T ÷ tan A for fitting angle A. The fittings turn by the roll angle, arctan(roll ÷ rise), measured from vertical. With the run known, the angle is arctan(T ÷ run) and the travel is √(T² + run²).
Example: 12" of rise and 16" of roll with 45° fittings. True offset = √(12² + 16²) = √(144 + 256) = √400 = 20". Travel = 20 × 1.414 = 28.28" (28 5/16"), run = 20 × 1.000 = 20", and the fittings roll arctan(16 ÷ 12) = 53.1° off vertical.
Measure rise and roll center to center between the two parallel runs. The travel is fitting center to fitting center, so subtract both take-outs to get the cut length. With no roll the answer is a plain vertical offset (roll angle 0°); with no rise the offset lies flat and the fittings are rolled 90°.
Frequently asked questions
How do you calculate a rolling offset?
Find the true offset first: √(rise² + roll²). Multiply it by the fitting's travel multiplier (1.414 for 45s, 2.613 for 22½s) for the travel, and by the run multiplier (1.000 for 45s, 2.414 for 22½s) for the run. 12" rise and 16" roll with 45s: true offset 20", travel 28.28", run 20".
What is the true offset in a rolling offset?
The straight-line distance between the centerlines of the two parallel runs, seen looking along the pipe. It is the diagonal of the rise and the roll: 9" of rise and 12" of roll give √(81 + 144) = √225 = 15".
How do you figure a rolling offset with 22 1/2 degree fittings?
The same steps with the 22½° multipliers. 9" rise and 12" roll: true offset 15", travel 15 × 2.613 = 39.20" (39 3/16"), run 15 × 2.414 = 36.21" (36 3/16").
How far do I roll the fitting?
Turn it arctan(roll ÷ rise) away from vertical, toward the roll side. 12" rise and 16" roll: arctan(1.333) = 53.1°. With no roll the angle is 0° (a plain vertical offset); with no rise it is 90°.
What fitting angle do I need when the run is fixed?
Angle = arctan(true offset ÷ run). 3" rise and 4" roll make a 5" true offset; over a 12" run that is arctan(5 ÷ 12) = 22.6°, with a 13" travel (√(25 + 144) = √169). An angle that is not a stock fitting means picking the nearest stock angle and changing the run, or cutting a fitting to that angle.