Conduit Shrink Calculator

A conduit shrink calculator determines the longitudinal distance lost when conduit is bent into an offset or equivalent bend set. The result is used during conduit layout to establish where bends must begin so the finished raceway lands at the intended box, stub-up, coupling, or alignment point.

For the entered geometry, the calculator produces:

• Estimated shrink per set
• Total estimated shrink
• Travel between bends
• Offset multiplier
• Shrink per inch of offset

Shrink is a layout value. It affects the marks placed on the conduit before bending; it does not change conductor ampacity, raceway fill, voltage drop, or the electrical load served by the branch circuit or feeder.

Offset Depth and Bend Angle

An offset moves conduit perpendicular to its original path. Offset depth is that perpendicular movement, entered in inches. Bend angle is the angle used by each bend in the bend set.

The bend angle controls two related layout values:

• The offset multiplier, used to determine travel between bends
• The shrink per inch of offset, used to determine the conduit length consumed by the offset geometry

A larger offset depth increases both travel and shrink. The selected bend angle changes the geometry and therefore changes the multiplier and shrink factor.

The calculator keeps this arithmetic within the selected offset or saddle workflow. It does not determine the order in which bends should be made.

Calculator Inputs

Input	Unit	Electrical layout use
Offset depth	in	The perpendicular distance the conduit must move from its original centerline
Bend angle	deg	The angle used by each bend set
Bend-set count	sets	The number of equivalent bend sets for which total shrink is required

The input values should describe the intended finished conduit path. Offset depth is not the distance between bend marks, and bend-set count is not a substitute for determining the actual field bend sequence.

Shrink and Travel Calculation

The calculator calculates shrink for one entered bend set, then multiplies that result by Bend-set count.

\(\displaystyle \text{Estimated shrink per set} = \text{Offset depth} \times \text{Shrink per inch of offset} ] = [ \text{Total estimated shrink} = \text{Estimated shrink per set} \times \text{Bend-set count}\)

Travel between bends is calculated from the offset depth and the displayed offset multiplier:

\(\displaystyle \text{Travel between bends} = \text{Offset depth} \times \text{Offset multiplier}\)

The displayed Angle used confirms the bend angle applied to the calculation.

Calculation Example

Enter the following values:

Input	Value
Offset depth	4 in
Bend angle	30 deg
Bend-set count	2 sets

The calculator returns:

Result	Value
Estimated shrink per set	1.0718 in
Total estimated shrink	2.1436 in
Travel between bends	8 in
Offset multiplier	2 x
Shrink per inch of offset	0.2679 x
Angle used	30 deg

For one 4-inch offset at a 30-degree bend angle:

\(\displaystyle 4\text{ in} \times 0.2679 = 1.0716\text{ in}\)

The displayed estimated shrink per set is 1.0718 in. With two equivalent bend sets:

\(\displaystyle 1.0718\text{ in} \times 2 = 2.1436\text{ in}\)

The travel between bends is:

\(\displaystyle 4\text{ in} \times 2 = 8\text{ in}\)

The layout implication is that two equivalent bend sets produce an estimated combined shrink of 2.1436 inches. That shrink must be accounted for when establishing the conduit’s starting position or bend marks relative to the required finished endpoint.

Field Layout Limits

The worksheet provides geometry-based shrink arithmetic only. Actual conduit installation still depends on the bend sequence, bender shoe markings, conduit size and type, field convention, and springback.

Verify the finished raceway position after bending, particularly where the conduit must enter a box, align with a parallel run, maintain clearance, or connect to a fixed enclosure. The calculation does not select a bending method or confirm installation requirements; those decisions remain part of the field layout and applicable project requirements.