Rolling Offset Calculator: Pipe Travel, True Offset and Run for 45°, 22½° and Other Fittings

How it works

true offset = √(set² + roll²) · travel = true offset ÷ sin(fitting angle) · run = true offset ÷ tan(fitting angle) · with a known run: travel = √(set² + roll² + run²), angle = atan(true offset ÷ run) · cut length = travel − 2 × take-out · roll angle = atan(roll ÷ set)

A rolling offset moves a pipe both up (the set) and sideways (the roll) at the same time with two fittings, so the offset piece runs diagonally through a box. Looking straight down the diagonal of the end of that box, the set and roll form a right triangle whose hypotenuse is the true offset, √(set² + roll²). From there it is a simple offset in one plane: the travel (the center-to-center length of the offset piece) is the true offset ÷ sin of the fitting angle, and the run it takes along the line is the true offset ÷ tan of the angle. For 45° fittings the multipliers are 1.414 and 1.000; for 22½° they are 2.613 and 2.414. If the run is fixed by a wall or another pipe, switch to “Run known”: the travel is √(set² + roll² + run²) and the calculator gives the fitting angle you need and the nearest standard fitting. Enter the take-out of your fittings under More options to get the actual pipe cut length, and use the roll angle to turn both fittings off plumb so they line up. Inch results show the nearest 1/16 in. Unlike the conduit offset bend calculator, which handles bends in one plane for electrical conduit, this one solves the three-dimensional offset that pipefitters, plumbers and sprinkler fitters build with 45° and other fittings. Measure set and roll center to center, and dry-fit before gluing, threading or welding.

Worked example

A pipe must move 12 in up and 16 in over using 45° fittings. The true offset is √(12² + 16²) = 20 in. The travel is 20 ÷ sin 45° = 20 × 1.4142 = 28.28 in (28 5/16 in) center to center, and the offset advances 20 ÷ tan 45° = 20 in along the line. Check: √(12² + 16² + 20²) = 28.28 in. Both fittings are turned atan(16 ÷ 12) = 53.1° off vertical.

Sources: Omni Calculator: Rolling offset (true offset, travel, run, multipliers and 100 × 50 cm example)

Frequently asked questions