---
title: "Rolling Offset Calculator for Conduit — True Offset & Marks | BendBoss"
description: "Rolling offset calculator: enter the rise and the roll to get the true offset (√(rise² + roll²)), the distance between bends, the shrink and the roll angle. Worked example and formula for EMT."
url: https://bendboss.app/rolling-offset-calculator/
language: en
last_reviewed: 2026-11-14
---

[BendBoss](https://bendboss.app/) › Rolling offset

# Rolling offset calculator

A rolling offset moves a conduit over and up (or down) at the same time. Instead of two separate offsets, you bend one offset whose depth is the diagonal of the rise and the roll — the true offset — with the conduit rolled to the right angle.

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

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

The true offset is the diagonal of the rise and roll box.

## The rolling offset formula

True offset = √(rise² + roll²)  
Distance between bends = true offset × multiplier  
Shrink = true offset × shrink per inch  
Roll angle = arctan(roll ÷ rise)

It's the Pythagorean theorem: the rise and roll are the two sides of a right triangle and the true offset is the hypotenuse. IBEW Local 903's Bending Book works it the same way (its example: 4″ and 3″ give a 5″ offset) and adds a field shortcut — mark the rise and the roll on a framing square and measure diagonally between the two marks. Then bend the true offset as an ordinary offset.

## Worked example: 8″ rise, 6″ roll, 30° bends

  1. True offset: √(8² + 6²) = √100 = **10″**.
  2. Distance between bends: 10 × 2.00 = **20″**.
  3. Shrink: 10 × ¼″ = **2 1/2″**.
  4. Roll angle: arctan(6 ÷ 8) ≈ **36.9°** from vertical.
  5. Mark and bend as a 10″ offset with the conduit rolled about 37° off vertical.

## Quick true-offset table

Rise × roll| True offset| Between bends at 30°  
---|---|---  
3″ × 4″| 5″| 10″  
4″ × 4″| 5 11/16″| 11 5/16″  
6″ × 6″| 8 1/2″| 17″  
6″ × 8″| 10″| 20″  
8″ × 8″| 11 5/16″| 22 5/8″  
5″ × 12″| 13″| 26″  
10″ × 10″| 14 1/8″| 28 5/16″  
12″ × 12″| 17″| 33 15/16″  
  
## Setting the roll in the field

Mark the conduit's top centerline, then rotate it by the roll angle before the first bend. A torpedo level with an angle vial or an angle finder on the conduit gets you close; a full 45° roll is exactly halfway between vertical and horizontal. Keep the second bend in the same plane as the first.

## Common questions

### How do you calculate a rolling offset?

Find the true offset with √(rise² + roll²), then multiply it by the multiplier for your angle to get the distance between bends. Shrink is true offset × shrink per inch.

### What is the true offset of a 6″ rise and 8″ roll?

10″. √(36 + 64) = √100 = 10. At 30° the marks are 20″ apart.

### How much do I roll the conduit?

arctan(roll ÷ rise) from vertical. Equal rise and roll means a 45° roll.

### Is a rolling offset the same as two offsets?

It replaces two offsets with one, which saves conduit, bends and pulling effort.

## Sources

  * [IBEW Local 903, Bending Book rev. 2](https://lu903.com/wp-content/uploads/2017/06/Bending-Book-rev-2-full.pdf)
  * [Greenlee, Aluminum and Iron Site-Rite® Hand Benders Use Guide, 52034125 REV 02 (2023)](https://cdn.greenlee.com/resources/media?key=1adba548-f1d2-43d2-bf44-fe4b89a8b579&languageCode=en&type=document)

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## Related bend guides

  * [Offset calculator](https://bendboss.app/offset-calculator/)
  * [Offset multiplier & shrink chart](https://bendboss.app/offset-multiplier-chart/)
  * [Parallel offsets](https://bendboss.app/parallel-offset-calculator/)
  * [Compound 90](https://bendboss.app/compound-90/)
  * [The BendBoss app](https://bendboss.app/conduit-bending-app/)