Conduit Bending Math

Conduit bending is where geometry meets the job site. Every offset, saddle, and stub-up requires a calculation to get the bend right the first time. The math is straightforward once you know the multipliers and shrink constants.

Offset Bends

An offset bend changes the conduit’s path from one plane to another — for example, going around an obstruction or transitioning from a surface-mounted run to a recessed panel. An offset uses two equal bends in opposite directions.

The Offset Formula

$\text{Travel} = \text{Offset depth} \times \text{Multiplier}$

Where:

• Offset depth = the perpendicular distance the conduit needs to move (in inches)
• Travel = the distance between the two bend marks on the conduit
• Multiplier = depends on the bend angle (from trigonometry: $\text{multiplier} = \frac{1}{\sin(\theta)}$)

Offset Multipliers

Most common on the job: 30-degree offsets (easy multiplier of 2.0) and 45-degree offsets (for larger obstacles).

What Is Shrink?

When you bend an offset, the conduit gets “shorter” — the distance from the end of the conduit to the first bend decreases. You must account for this shrink when measuring your first bend mark.

$\text{Shrink} = \text{Offset depth} \times \text{Shrink constant}$

For a 30-degree offset with a 4-inch depth: $\text{Shrink} = 4 \times \frac{1}{4} = 1$ inch. Add 1 inch to your first mark.

Worked Examples

Example 1: 4-Inch Offset at 30 Degrees

Scenario: You need to offset a conduit run 4 inches to clear a beam. You choose 30-degree bends.

Step 1 — Calculate travel (distance between marks):

$\text{Travel} = 4 \times 2.0 = 8 \text{ inches}$

Step 2 — Calculate shrink:

$\text{Shrink} = 4 \times 0.25 = 1 \text{ inch}$

Step 3 — Mark the conduit:

• First mark: measure from the end of the conduit to where the offset needs to start, then add 1 inch for shrink
• Second mark: 8 inches from the first mark

Answer: Place bends 8 inches apart and add 1 inch of shrink to the first mark.

Example 2: 6-Inch Offset at 45 Degrees

Scenario: A large obstacle requires a 6-inch offset. You use 45-degree bends for a tighter transition.

Travel:

$\text{Travel} = 6 \times 1.414 = 8.48 \approx 8\frac{1}{2} \text{ inches}$

Shrink:

$\text{Shrink} = 6 \times 0.375 = 2.25 \approx 2\frac{1}{4} \text{ inches}$

Answer: Marks are 8-1/2 inches apart, with 2-1/4 inches of shrink added to the first mark.

Example 3: Small Offset at 22.5 Degrees

Scenario: You need a 3-inch offset to bring a conduit run off a wall to clear a shallow box. You use 22.5-degree bends for a gradual transition.

Travel:

$\text{Travel} = 3 \times 2.6 = 7.8 \approx 7\frac{3}{4} \text{ inches}$

Shrink:

$\text{Shrink} = 3 \times 0.1875 = 0.5625 \approx \frac{9}{16} \text{ inch}$

Answer: Marks are approximately 7-3/4 inches apart, with about 9/16 inch of shrink.

Saddle Bends (Three-Bend Saddle)

A saddle bend goes over an obstruction and returns to the original plane. It uses a center bend (usually 45 degrees) and two return bends (usually 22.5 degrees each).

Three-Bend Saddle Marks

1. Center mark at the center of the obstruction
2. Outer marks on each side of center: $\text{Distance from center} = \text{Obstruction depth} \times 2.5$ (for 45/22.5 combination)
3. Shrink for a three-bend saddle: $\text{Obstruction depth} \times \frac{3}{16}$ inch per inch

Four-Bend Saddle

A four-bend saddle uses two offset bends in sequence. Calculate each offset separately using the standard offset formula, then combine.

Reference Table: Common Bends

90-Degree Stub-Up Deduct Values

Practice Problems

Test your understanding with these problems. Click to reveal each answer.

Common Mistakes to Avoid

1. Forgetting shrink. If you do not add the shrink value to your first mark, the conduit will end up short. This is the most common bending error.
2. Using the wrong multiplier. The multiplier for 30 degrees is 2.0, not 1.5 or 3.0. Memorize the five common values.
3. Measuring travel as the offset depth. The travel is always longer than the offset depth (except at 90 degrees, which is not an offset). A 4-inch offset at 30 degrees has 8 inches of travel, not 4.
4. Not accounting for the bender’s take-up. Different benders have different take-up marks. Always verify your bender’s specifications against the manufacturer’s chart.
5. Bending past the desired angle. Overbending kinks the conduit. Bend slowly, check the angle with a protractor or level, and stop at the exact angle.

Key Takeaways

• The offset formula is $\text{Travel} = \text{Offset depth} \times \text{Multiplier}$
• Memorize the five common multipliers: 10-degree = 6.0, 22.5-degree = 2.6, 30-degree = 2.0, 45-degree = 1.414, 60-degree = 1.155
• Always add shrink to the first bend mark to prevent the conduit from ending up short
• The 30-degree offset is most common because the multiplier of 2.0 makes math easy on the job
• For stub-ups, subtract the deduct value from the desired stub height to find the mark location

Math for Electricians