What is a rolling offset?

A rolling offset is when a pipe must shift both sideways and up or down at the same time, so the connecting piece runs diagonally in three dimensions. The true offset is the straight-line distance combining the horizontal roll and the vertical rise.

How is the travel length calculated?

First the true offset is the square root of roll squared plus rise squared. Then the travel, the length of the diagonal pipe between fitting centers, equals the true offset divided by the sine of the fitting angle. For a 45 degree fitting that is the true offset times 1.414.

What is fitting take-out?

Take-out is the laying length a fitting consumes, measured from the center of the fitting to the face where the pipe seats. The center-to-center travel must be reduced by the take-out of both fittings to get the actual pipe cut length.

Why use 22.5 degree fittings instead of 45?

Shallower angles like 22.5 degrees create a longer, gentler diagonal that improves drainage flow and reduces turbulence, at the cost of more travel length and space. Fitting angle choice balances flow, space, and the available fitting inventory.

Does the order of roll and rise matter?

No. The true offset combines them with the Pythagorean theorem, which is symmetric, so swapping roll and rise gives the same true offset and travel. The spread, or the individual horizontal and vertical legs, will differ in orientation but not in magnitude.

Plumbing Fitting Angle & Rolling Offset Calculator

A rolling offset is the pipefitter’s classic puzzle: a pipe that must move sideways and up or down at once, connected by a diagonal piece running through three dimensions. This calculator solves it exactly, returning the true offset, the diagonal travel between fitting centers, and the cut length after fitting take-out.

How it works

The roll and rise form two legs of a right triangle whose hypotenuse is the true offset. The diagonal pipe travel then follows from the fitting angle:

true offset = √( roll² + rise² )
travel      = true offset / sin(fitting angle)
run (along axis) = true offset / tan(fitting angle)
cut length  = travel − (take-out of both fittings)

For the common 45 degree fitting, sin(45°) and tan(45°) both simplify nicely: travel equals the true offset times 1.414, and the run equals the true offset. Shallower 22.5 degree fittings produce a longer travel of about 2.61 times the true offset.

Example and notes

Suppose a pipe must roll 8 inches sideways and rise 6 inches, using 45 degree fittings. The true offset is √(8² + 6²) = 10 inches. The diagonal travel is 10 / sin(45°) = 14.14 inches center to center. If each fitting has a 1.5-inch take-out, the actual pipe cut is 14.14 − 3.0 = 11.14 inches. Always confirm take-out from your fitting’s laying-length chart, because it varies by pipe size, material, and fitting angle.