Rolling Offset: Formula, Calculation & How to Bend

A rolling offset is the bend that separates apprentices from journeymen. You need conduit to go up and over to the left at the same time, and a standard offset bend only handles one direction. When a conduit run has to change elevation and shift sideways between two points, you need a rolling offset. It's a 3D problem, and the math reflects that.

This guide covers the rolling offset formula, walks through the trigonometry behind it, and gives you step-by-step worked examples with real measurements. You'll also learn the common field scenarios where rolling offsets show up and the mistakes that waste conduit.

What Is a Rolling Offset?

A standard offset moves conduit in one plane. It goes up, or it goes sideways. A rolling offset moves conduit in two planes simultaneously. The conduit rises (or drops) vertically while also shifting horizontally. Think of it as a diagonal move through 3D space.

Here's a common scenario. You're running 3/4" EMT along a wall at 8 feet high. The conduit needs to reach a junction box that's 6 inches higher and 4 inches to the left. You can't just bend up and then bend sideways. That would use four bends (two offsets) and eat up 120 degrees of your NEC 360-degree allowance between pull points. A single rolling offset does it in two bends, using only 60 degrees at 30-degree angles.

The key difference from a flat offset is that you're working with a triangle in 3D space. The rise and roll form two legs of a right triangle, and the hypotenuse is what you actually need to bend around. That hypotenuse is called the true offset.

The Rolling Offset Formula

Every rolling offset calculation starts with finding the true offset. This is pure Pythagorean theorem.

Step 1: Find the True Offset

True Offset = √(Rise² + Roll²)

• Rise = the vertical distance between the start and end points of the conduit
• Roll = the horizontal distance the conduit shifts sideways
• True Offset = the actual diagonal distance the conduit must bridge

If the rise is 6" and the roll is 4", the true offset is √(36 + 16) = √52 = 7.21". That 7.21" is the number you'll use with the multiplier, not the 6" or the 4".

Step 2: Calculate the Distance Between Bends

Distance Between Bends = True Offset x Multiplier

The multiplier depends on the bend angle, just like a standard offset. The multiplier chart values are the same ones you already know:

Rolling offset multipliers and shrink constants by bend angle

Bend Angle	Multiplier	Shrink per Inch of True Offset
10°	5.759	1/16"
15°	3.864	1/8"
22.5°	2.613	3/16"
30°	2.000	1/4"
45°	1.414	3/8"
60°	1.155	1/2"

Most electricians use 30 degrees for rolling offsets. The math is clean (multiplier of 2.0) and the shrink is easy to calculate (1/4" per inch). The 30-degree angle also keeps bend degree consumption reasonable for the NEC (NFPA 70) 360-degree limit.

Step 3: Calculate Shrink

Shrink = True Offset x Shrink Constant

Shrink works the same way as a standard offset, but you apply it to the true offset, not the rise or roll individually. At 30 degrees, the shrink is 1/4" per inch of true offset. For our 7.21" true offset, shrink = 7.21 x 0.25 = 1.80", or roughly 1-13/16".

Worked Example 1: Basic Rolling Offset

You're running 1" EMT along a ceiling and need to drop down 6 inches while shifting 8 inches to the right to enter a panel. You'll use 30-degree bends.

Step 1: Measure rise and roll

• Rise: 6"
• Roll: 8"

Step 2: Calculate the true offset

True Offset = √(6² + 8²) = √(36 + 64) = √100 = 10"

This is a clean 3-4-5 right triangle scaled up. The true offset is exactly 10 inches.

Step 3: Calculate the distance between bends

Distance = 10" x 2.0 = 20"

Step 4: Calculate shrink

Shrink = 10" x 1/4" = 2-1/2"

Step 5: Mark the conduit

Say the first bend needs to start 36" from the end of the conduit. Add the shrink: 36" + 2-1/2" = 38-1/2". That's your first mark. The second mark goes at 38-1/2" + 20" = 58-1/2".

Step 6: Determine the rotation angle

The conduit doesn't just bend in a flat plane. You need to know how much to rotate between the two bends. The rotation angle comes from the rise and roll:

Rotation Angle = arctan(Roll / Rise) = arctan(8 / 6) = 53.1°

This tells you the conduit must be rotated 53.1 degrees from vertical when you make the bends. In the field, you'd measure this with a protractor or angle finder, or use a reference line on the conduit.

Step 7: Make the bends

1. Place the first mark on the bender arrow. Bend to 30 degrees.
2. Flip the conduit. Rotate it so the bend points toward the final position (53.1 degrees from vertical in this case).
3. Align the second mark on the arrow. Bend to 30 degrees.
4. Sight down the conduit to verify alignment. The end should point 6" lower and 8" to the right of where it started.

Worked Example 2: Rack to Junction Box

This one comes up constantly on commercial jobs. You're pulling conduit off a rack and need to reach a junction box that's 3 inches lower and 5 inches to the left. The first bend starts 24 inches from the end. You'll use 30-degree bends.

Step 1: Measure rise and roll

• Rise: 3"
• Roll: 5"

Step 2: Calculate the true offset

True Offset = √(3² + 5²) = √(9 + 25) = √34 = 5.83"

Step 3: Calculate the distance between bends

Distance = 5.83" x 2.0 = 11-11/16" (11.66")

Step 4: Calculate shrink

Shrink = 5.83" x 1/4" = 1-7/16" (1.46")

Step 5: Mark the conduit

• First mark: 24" + 1-7/16" = 25-7/16"
• Second mark: 25-7/16" + 11-11/16" = 37-1/8"

Step 6: Find the rotation angle

Rotation = arctan(5 / 3) = 59.0°

Step 7: Bend and check

Make both 30-degree bends with the conduit rotated 59 degrees from vertical. Verify the conduit reaches the box location. If you're off, the rotation angle is usually the culprit, not the math.

Rolling Offset vs. Two Separate Offsets

You could achieve the same result by making two separate offsets: one vertical and one horizontal. But there are good reasons to use a rolling offset instead.

Rolling offset compared to using two separate offsets for the same directional change

Factor	Rolling Offset	Two Separate Offsets
Total bends	2	4
Degrees used (at 30°)	60°	120°
NEC 360° impact	Uses 17% of allowance	Uses 33% of allowance
Wire pulling difficulty	Easier (fewer bends)	Harder (more friction)
Conduit length used	Less	More
Calculation difficulty	Requires trigonometry	Simple multiplier math
Field execution	Requires rotation skill	Standard flat bends

As EC&M's conduit bending guide notes, a rolling offset at 30 degrees uses 60 degrees total, while two separate 30-degree offsets use 120 degrees. That's half the bend degrees for the same result. On a long run with multiple direction changes, those saved degrees are the difference between reaching your destination and needing another pull box.

How to Do This in the Conduit Bending App

The rolling offset calculation involves square roots, arctangents, and shrink adjustments. Doing it on paper is fine when you have time, but on the job site with multiple runs to calculate, you want it done in seconds.

Conduit Bending has a dedicated rolling offset calculator built in. Open the Conduit Bending app and select Rolling Offset. Enter the rise and roll, pick your bend angle, and the app gives you:

• True offset (the calculated hypotenuse)
• Distance between bends
• Shrink amount
• Both mark locations on the conduit
• Rotation angle for field alignment

The app handles all 16 bend types and stores bender-specific data for EMT, IMC, and rigid conduit from 1/2" to 4". You can also try the free online Rolling Offset Calculator right in your browser.

Common Field Scenarios

Rolling offsets don't show up randomly. There are specific situations on the job site where they're either required or strongly preferred.

Transitioning Between Rack Levels

When conduit moves from one tray or rack to another that's both higher and offset to one side, a rolling offset is the cleanest solution. You'll see this in mechanical rooms and data centers where racks at different elevations carry different circuits.

Dropping from Ceiling to Wall

Conduit running along a ceiling that needs to reach a panel or box on a wall often requires both a vertical drop and a horizontal shift. Two separate offsets would use excessive bend degrees. A single rolling offset gets there efficiently.

Turning a Corner at a Different Elevation

According to EC&M, rolling offsets are practical when the conduit run is parallel to the corner to be turned. If you need to go around a corner and change height at the same time, the rolling offset handles both in one move.

Parallel Runs with Stacked Conduits

When multiple conduits in a rack need to reach destinations at different heights and horizontal positions, each one may need its own rolling offset with different rise and roll values. This is where having the Rolling Offset Calculator saves real time.

Common Mistakes

Rolling offsets go wrong more often than standard offsets because there's an extra dimension to get right. Here are the errors that waste the most conduit.

• Using rise or roll instead of true offset: The single most common mistake. If your rise is 6" and your roll is 8", the multiplier gets applied to 10" (the true offset), not to 6" or 8". Applying the multiplier to just the rise gives you a bend that's too short to reach the destination.
• Forgetting to calculate the rotation angle: You can nail the true offset, the distance between bends, and the shrink perfectly, but if you don't rotate the conduit correctly between bends, the endpoint will be off. The rotation is arctan(roll/rise) from vertical. Skip this and the conduit will end up in the wrong position.
• Confusing rise and roll in the arctan formula: The rotation from vertical is arctan(roll/rise), not arctan(rise/roll). Getting these backwards will rotate your conduit the wrong amount. Double-check which measurement is vertical and which is horizontal before calculating.
• Applying shrink to the wrong value: Shrink applies to the true offset, not to the rise, roll, or distance between bends. At 30 degrees, shrink = true offset x 1/4".
• Not keeping bends in the same rotated plane: Both bends must be in the same plane, which is rotated from horizontal. If you bump the conduit between bends or don't rotate consistently, the conduit will twist and the far end won't line up. Use pencil lines girded around the conduit as alignment references, as recommended in Mike Holt's hand bending guide.
• Overbending and trying to correct: If you go past your angle, don't bend it back. Reverse bending weakens EMT and creates visible kinks. Cut a new piece. Conduit is cheap compared to the time you'll spend fighting a bad bend.

Quick Reference: Rolling Offset Values

This table gives pre-calculated true offsets for common rise and roll combinations. All values assume 30-degree bends (multiplier = 2.0, shrink = 1/4" per inch of true offset).

Pre-calculated rolling offset values for common rise and roll combinations at 30 degrees

Rise	Roll	True Offset	Between Bends	Shrink	Rotation
2"	2"	2-13/16"	5-5/8"	11/16"	45.0°
3"	4"	5"	10"	1-1/4"	53.1°
4"	3"	5"	10"	1-1/4"	36.9°
4"	6"	7-3/16"	14-3/8"	1-13/16"	56.3°
6"	4"	7-3/16"	14-3/8"	1-13/16"	33.7°
6"	6"	8-1/2"	17"	2-1/8"	45.0°
6"	8"	10"	20"	2-1/2"	53.1°
8"	6"	10"	20"	2-1/2"	36.9°
10"	8"	12-13/16"	25-5/8"	3-3/16"	38.7°
12"	6"	13-7/16"	26-7/8"	3-3/8"	26.6°

For combinations not listed here, use the Rolling Offset Calculator or the Conduit Shrink Calculator for exact values. The conduit fill chart can also help you size the conduit before you start bending.

Tips for Getting Rolling Offsets Right

Rolling offsets have a reputation for being difficult, but most of that reputation comes from skipping steps. Follow these practices and they'll go smoothly.

• Always find the true offset first. Don't try to shortcut the Pythagorean theorem. Rise and roll are not interchangeable with the true offset. The math takes 10 seconds with a calculator.
• Draw a reference line along the conduit. Before bending, draw a straight pencil line from end to end. After each bend, check that the line is still straight. If it's not, the conduit has rotated, and the bend will be off.
• Use 30-degree bends when possible. The multiplier of 2.0 and shrink of 1/4" per inch are the easiest values to work with in your head. Save 45-degree bends for situations where space is tight.
• Measure twice, bend once. With rolling offsets, a measurement error gets amplified because it feeds into the square root, the multiplier, and the shrink. Check your rise and roll measurements before you start calculating.
• Keep a calculator handy. You need square roots for rolling offsets. Mental math won't get you there reliably. A phone calculator works, but the Rolling Offset Calculator gives you everything in one step.
• Practice on scrap conduit. If you're new to rolling offsets, bend a few practice pieces before you cut into good material. Get the rotation angle dialed in on scrap so you know what it feels like when it's right.

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Frequently Asked Questions

What is a rolling offset in conduit bending?

A rolling offset is a conduit bend that changes direction in two planes at the same time. Instead of going only up or only sideways, the conduit moves both vertically and horizontally between two points. It combines a rise (vertical change) and a roll (horizontal change) into a single offset. The true offset distance is calculated using the Pythagorean theorem: True Offset = √(rise² + roll²).

What is the rolling offset formula?

The rolling offset formula has two parts. First, calculate the true offset: True Offset = √(rise² + roll²). Then calculate the distance between bends: Distance Between Bends = True Offset x Multiplier. The multiplier depends on your bend angle. At 30 degrees the multiplier is 2.0, at 22.5 degrees it is 2.613, and at 45 degrees it is 1.414.

How do you calculate a rolling offset?

Measure the vertical rise (how far up) and the horizontal roll (how far sideways) between your start and end points. Square both numbers, add them together, and take the square root. That gives you the true offset. Multiply the true offset by the multiplier for your bend angle to get the distance between bends. Then calculate shrink and mark the conduit just like a standard offset.

Why is a rolling offset harder than a regular offset?

A regular offset changes direction in one plane only, so you measure one distance and apply the multiplier directly. A rolling offset changes direction in two planes, which means you need to find the true diagonal distance using trigonometry before you can apply the multiplier. The conduit also needs to be rotated between bends so it exits at the correct angle, which requires careful alignment that a standard offset does not.

Does a rolling offset use more bend degrees than two separate offsets?

No, it uses far less. A single rolling offset at 30 degrees uses 60 degrees total (two 30-degree bends). If you used two separate offsets to achieve the same result, one horizontal and one vertical, each at 30 degrees, that would be 120 degrees total (four 30-degree bends). The rolling offset saves 60 degrees of your NEC 360-degree bend allowance between pull points.