---
title: "Parallel Offset Calculator — Mark Shift for Conduit Racks | BendBoss"
description: "Parallel offset calculator for conduit racks: shift each run's marks by center-to-center spacing × tan(angle ÷ 2) so spacing stays even through the bend. Includes mixed-size EMT spacing from ANSI C80.3 diameters."
url: https://bendboss.app/parallel-offset-calculator/
language: en
last_reviewed: 2026-11-14
---

[BendBoss](https://bendboss.app/) › Parallel offsets

# Parallel offset calculator

When several conduits are offset together, bending them all at the same marks pinches the rack in the middle of the offset. Shift each following run's marks by the spacing times the tangent of half the bend angle and they stay evenly spaced all the way through.

Last reviewed Nov 14, 2026 · Sources at the end of the page

_Interactive calculator on the web page: https://bendboss.app/parallel-offset-calculator/_

Each run's marks move by the same shift, so the rack stays parallel through the offset.

## The parallel offset formula

Shift per run = center-to-center spacing × tan(bend angle ÷ 2)  
Run n marks = run 1 marks + (n − 1) × shift

IBEW Local 903's Bending Book states it directly: "multiply the (C-C) measurement of the conduits by the tangent of ½ the bend angle" and advance each succeeding conduit's bends by that figure. Their example: 2″ centers at 30° → 0.2679 × 2″ = 0.536″, about 9/16″.

## Worked example: 3 runs at 2″ centers, 30°

  1. tan(15°) = 0.268. Shift = 2″ × 0.268 = **9/16″**.
  2. Run 1: lay out a normal [offset](https://bendboss.app/offset-calculator/).
  3. Run 2: both marks 9/16″ farther from the end. Run 3: both marks **1 1/16″** farther.

## Shift per inch of spacing

Angle| tan(θ ÷ 2)| Shift at 2″ centers| Shift at 3″ centers  
---|---|---|---  
10°| 0.087| 3/16″| 1/4″  
22½°| 0.199| 3/8″| 5/8″  
30°| 0.268| 9/16″| 13/16″  
45°| 0.414| 13/16″| 1 1/4″  
60°| 0.577| 1 1/8″| 1 3/4″  
  
## Spacing mixed sizes in one rack

When the runs are different sizes, the center-to-center spacing is half of each conduit's outside diameter plus the gap you want between them. With a 1″ gap:

Pair (EMT)| Center-to-center with 1″ gap  
---|---  
1/2″ + 1/2″| 1 11/16″  
1/2″ + 3/4″| 1 13/16″  
3/4″ + 3/4″| 1 15/16″  
3/4″ + 1″| 2 1/16″  
1″ + 1″| 2 3/16″  
1/2″ + 2″| 2 7/16″  
1-1/4″ + 1-1/4″| 2 1/2″  
2″ + 2″| 3 3/16″  
Spacing = (OD₁ + OD₂) ÷ 2 + gap, using ANSI C80.3 nominal outside diameters.

The BendBoss app does this per pair for every run in the rack — including mixed sizes — and applies the shift automatically.

## Common questions

### How do you calculate parallel offsets?

Lay out the inside run as a normal offset. Shift each next run's marks by center-to-center spacing × tan(angle ÷ 2), adding one more shift per run.

### What is the shift for 30° parallel offsets?

0.268 × the spacing. At 2″ centers that's about 9/16″ per run (IBEW Local 903 Bending Book).

### Why not just use the same marks on every conduit?

The outside runs travel farther through the bend. Identical marks pinch the rack together inside the offset.

### Does conduit size change the shift?

No. The shift depends only on the spacing and the angle. Size affects the spacing itself — use the outside diameters.

## Sources

  * [IBEW Local 903, Bending Book rev. 2](https://lu903.com/wp-content/uploads/2017/06/Bending-Book-rev-2-full.pdf)
  * [ANSI C80.3 (NEMA), Steel Electrical Metallic Tubing — nominal outside diameters](https://webstore.ansi.org/preview-pages/NEMA/preview_C80.3+HTRJIBA.pdf)

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## Related bend guides

  * [Offset calculator](https://bendboss.app/offset-calculator/)
  * [Offset multiplier & shrink chart](https://bendboss.app/offset-multiplier-chart/)
  * [Rolling offset](https://bendboss.app/rolling-offset-calculator/)
  * [Kick](https://bendboss.app/kick-calculator/)
  * [The BendBoss app](https://bendboss.app/conduit-bending-app/)