Rolling Offset Calculator

A rolling offset occurs when conduit must clear an obstruction in two planes at once — for example, routing around a beam that requires both a horizontal shift and a vertical shift between two points on the same run. Unlike a standard offset, which moves conduit in a single plane, a rolling offset combines horizontal and vertical displacement into one diagonal bend set. The calculator converts these two displacement values into the single true offset dimension a bender actually needs, along with the travel distance between bends and the shrink allowance to add back into the cut length.

Inputs and Their Role

The calculator uses four fields, each representing a measurable condition on the job:

• Horizontal offset — the lateral displacement the conduit must cover, measured in inches.
• Vertical offset — the displacement in the perpendicular plane, also in inches.
• Bend angle — the angle used for both bends in the rolling offset, in degrees. Both bends must use the same angle for the geometry to hold.
• First mark — the reference distance from a fixed starting point (such as a coupling or box) to where the first bend mark will be made, in inches.

These are field measurements, not conduit specifications — the tool does not account for conduit size, material, or raceway fill.

True Rolling Offset

Because the horizontal and vertical offsets occur in different planes, they cannot simply be added. The true rolling offset is the diagonal distance the conduit must travel to satisfy both displacements simultaneously, found with the Pythagorean relationship:

True offset = √(horizontal offset² + vertical offset²)

With a horizontal offset of 3 in and a vertical offset of 4 in:

√(3² + 4²) = √(9 + 16) = √25 = 5 in

This 5-inch figure is the offset dimension used in the next calculation — it is not the horizontal or vertical value alone, and using either of those instead of the true offset will produce an incorrectly sized bend.

Travel Between Bends

Travel is the straight-line distance between the two bend marks, measured along the conduit. It depends on the true offset and the bend angle, using the cosecant relationship standard to offset bending:

Travel = True offset × csc(bend angle)

At a 30° bend angle, csc(30°) = 2.000, so:

Travel = 5 in × 2.000 = 10 in

Smaller bend angles increase the multiplier and produce a longer, gentler travel distance; larger angles shorten travel but tighten the bend radius requirement.

Mark Placement

First mark is a user-supplied reference point — in this example, 10 in from the fixed starting reference. The second mark is calculated by adding the travel distance to the first mark:

Second mark = First mark + Travel

10 in + 10 in = 20 in

These two marks are where the bends are made on the conduit, not where the obstruction begins or ends — the marks must be laid out from a consistent, identifiable reference point (box, coupling, or existing bend) to keep the offset centered correctly in the field.

Estimated Shrink

Bending conduit shortens its overall developed length compared to a straight measurement between endpoints. Shrink compensates for this by adding length back to the cut piece so the finished offset lands at the correct total distance. Shrink is derived from the true offset and a bend-angle-based shrink constant (0.268 in per inch of offset at 30°):

Shrink = 5 in × 0.268 = 1.3397 in

This value should be added to the overall cut length of the conduit before bending so the finished piece reaches the intended endpoint after the bends are formed.

Field and Geometry Limitations

This tool performs offset geometry only — it assumes both bends use the identical angle entered, that the conduit remains rigid and unobstructed along the calculated travel path, and that the operator applies a bender-specific technique (hand bender, mechanical, or hydraulic) separately, since bending method, radius, and take-up figures are not part of this calculation. It does not evaluate raceway fill, conduit size, support spacing, or code-mandated bend limits per run — those checks remain the responsibility of the installer against manufacturer bending charts and the AHJ‘s adopted code. Field verification of the fixed reference point, tape measurement accuracy, and bend angle consistency between the two bends is required before cutting, since small angle deviations compound across the travel distance and shift the second mark location.