Conduit Stub Length Calculator

A conduit stub length calculation establishes the layout distance needed to produce a required perpendicular rise when the bend angle, bender take-up allowance, and end allowance are known separately. The calculation produces three related field values:

• Tangent run: the straight geometric run required to reach the specified Stub height at the selected Bend angle
• Layout mark from end: the mark location after accounting for the Bender take-up allowance
• Recommended stub allowance: the total planning allowance after adding the separate End allowance

This calculation supports conduit bending layout for raceway terminations, offsets from a conduit end, fabricated stub sections, and installations where the actual bender reference point or take-up value must be handled explicitly. It does not determine conductor ampacity, raceway fill, voltage drop, branch-circuit sizing, feeder sizing, or conductor bending-space compliance; those electrical design items remain separate from the bend-layout geometry.

Stub Height and Bend Geometry

Stub height is the perpendicular distance the finished conduit stub must rise. The calculation converts that perpendicular height into a straight-line horizontal layout component called the Tangent run.

The conversion depends on the Bend angle. A lower bend angle requires a longer tangent run to reach the same stub height. A higher bend angle reaches that height over a shorter tangent run.

\(\displaystyle \text{tangent run} = \frac{\text{stub height}}{\tan(\text{bend angle})}\)

Use the angle actually intended for the bend and enter it in degrees. The geometric result is based on the tangent relationship only; it does not independently model the bend radius, conduit type, shoe geometry, or springback.

Bender Take-Up Allowance

The Bender take-up allowance is entered separately because the field reference used by a hand bender, mechanical bender, or fabrication method can shift the required layout mark. Take-up values are not interchangeable between all benders, conduit sizes, conduit materials, or bending methods.

The calculator adds the entered take-up value to the tangent run:

\(\displaystyle \text{layout mark from end} = \text{bender take-up allowance} + \text{tangent run}\)

The resulting Layout mark from end is the planned mark distance measured from the conduit end using the project’s stated bender reference method. Confirm whether the bender’s arrow, star, rim notch, center-of-bend mark, or another reference is being used before transferring the mark to conduit.

End Allowance

The End allowance accounts for a separate fabrication or termination allowance, such as a coupling, fitting, or project-specific end condition. It is not included in the tangent geometry and is not included in the layout mark unless the field method calls for it separately.

\(\displaystyle \text{recommended stub allowance} = \text{tangent run} + \text{bender take-up allowance} + \text{end allowance}\)

The Recommended stub allowance provides a total planning dimension when the finished conduit section needs material beyond the geometry and bender reference allowance. Verify the actual fitting engagement, coupling arrangement, and cut reference before using this value as a final cut length.

Calculation Example

For the following inputs:

Field	Entered value
Stub height	12 in
Bend angle	30 deg
Bender take-up allowance	6 in
End allowance	2 in

First, resolve the 12-inch perpendicular rise at a 30-degree bend angle:

\(\displaystyle \text{tangent run} = \frac{12}{\tan(30^\circ)} = 20.7846\text{ in}\)

Next, add the 6-inch bender take-up allowance:

\(\displaystyle \text{layout mark from end} = 6 + 20.7846 = 26.7846\text{ in}\)

Then add the separate 2-inch end allowance:

\(\displaystyle \text{recommended stub allowance} = 20.7846 + 6 + 2 = 28.7846\text{ in}\)

Result	Value
Tangent run	20.7846 in
Layout mark from end	26.7846 in
Recommended stub allowance	28.7846 in
Stub height used	12 in
Bend angle used	30 deg

For this layout, 26.7846 inches is the calculated mark location from the conduit end based on the entered bender take-up. The 28.7846-inch recommended stub allowance includes the additional 2-inch end allowance for the stated fabrication condition.

Field Verification

The calculation resolves the entered geometry and allowances; it does not replace field verification. Confirm the actual bender take-up for the conduit and bender in use, the end reference being measured, the fitting or coupling requirement, conduit cut condition, springback, and finished field dimensions.

A completed conduit run may also require separate review for raceway routing, box and fitting compatibility, conductor pulling conditions, raceway fill, conductor ampacity, voltage-drop design, support requirements, and applicable AHJ requirements.