Rolling offset geometry
Rolling Offset Travel Calculator
Calculate the true diagonal travel and roll angle for a conduit rolling offset before selecting bend spacing.
Calculate Rolling Offset Travel
Enter horizontal and vertical movement to calculate true offset travel and bend-plane roll angle.
Result
True offset
7.211 in
Diagonal used for rolling-offset spacing and shrink.
Roll angle
56.3 degrees
Bend-plane rotation from vertical toward the horizontal movement.
Result notes
Keep the entered values, assumptions, and result together when adding this calculation to job notes or submittal records. Final installation choices should align with the applicable code edition, equipment listing, manufacturer instructions, local amendments, and AHJ requirements.
Related calculators
Parallel Roll Offset Calculator
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Offset Bend Calculator
Field-chart geometry screen for bend spacing, shrinkage allowance, travel, and optional bend-mark layout.
Concentric Bend Spacing Calculator
Calculate centerline spacing for concentric conduit bends and parallel raceway layout checks.
Related charts
Parallel Roll Offset Chart
Use a parallel roll offset chart to document horizontal offset, vertical offset, true offset, roll angle, mark spacing, and rotation direction.
Offset Bend Multiplier Chart
Use offset multiplier chart: 15 deg = 3.9, 22.5 deg = 2.6, 30 deg = 2.0 and 45 deg = 1.414; a 4 in offset at 30 deg marks 8 in.
Concentric Bend Spacing Chart
Use this concentric bend spacing chart for 3/4 in EMT: 0.922 in OD + 1/2 in gap = 1.422 in centers, 12 in inner radius, and mark offsets.
Related guides
Conduit Fill Guide | 4 #6 THHN = 38.1%
Use conduit fill calculator example: 4 #6 THHN in 3/4 EMT uses 38.1%; compare NEC 40% fill, conductor count and ampacity derating.
Conduit Fill Table | 3/4 EMT #12, #10 and #6
Use this conduit fill table: 3/4 EMT fits 16 #12, 10 #10, 5 #8, or 4 #6 THHN at 40%; compare EMT, RMC and PVC sizes.
Formula and field context
Calculate the true diagonal travel and roll angle for a conduit rolling offset before selecting bend spacing.
Formula context
Parallel Roll Offset Chart
A rolling offset moves conduit in two directions at once, so spacing is based on the diagonal true offset rather than only the rise or side movement. The calculator combines horizontal and vertical offsets, applies the selected bend multiplier, and reports the roll angle needed to rotate the bend plane. Use this chart to keep rotation direction, mark spacing, and shrink tied together before bending.
Formula
True offset = sqrt(horizontal offset^2 + vertical offset^2). Roll angle = atan2(horizontal offset, vertical offset). Mark spacing = true offset x multiplier.Variables to keep with the result
- Horizontal offset is the side-to-side movement of the conduit centerline.
- Vertical offset is the rise or drop of the conduit centerline.
- True offset is the diagonal movement used for mark spacing and shrink.
- Roll angle is the rotation of the bend plane from vertical toward the horizontal offset.
Formula and variables
A rolling offset moves conduit horizontally and vertically at the same time, so the layout is based on the diagonal movement through space. The true offset formula is true offset = sqrt(horizontal offset^2 + vertical offset^2). The roll angle is roll angle = atan2(horizontal offset, vertical offset). Horizontal offset is the side-to-side movement, vertical offset is the rise or drop, and true offset is the value used later for mark spacing and shrink.
Field example
A conduit run that must move 6 in sideways and 4 in up has true offset = sqrt(6^2 + 4^2) = 7.211 in. The roll angle is atan2(6, 4), or about 56.3 degrees from vertical toward the horizontal movement. That true offset can then be used with a bend multiplier, such as 2.0 for a 30 degree bend, to find mark spacing in a separate layout step.
Assumptions and layout limits
This worksheet isolates the geometry of the rolling offset. It does not choose bend angle, calculate second mark location, account for shrink, or decide whether the roll should be left, right, up, or down from the installer position. Use it when the first question is the diagonal travel and roll angle, then use the parallel offset spacing tool or the full parallel roll offset calculator for mark layout.
Common mistakes
Common mistakes include using only the vertical rise as the offset, ignoring the side-to-side movement, recording roll angle without direction, and using true offset as if it were the finished mark spacing. Keep horizontal offset, vertical offset, true offset, roll angle, and rotation direction together before transferring marks to conduit.