Conduit Shrink Chart

Use this conduit shrink chart after a bending calculator result to document how much layout length is lost through an offset, saddle, kick, or rolling offset.

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Quick reference table

Conduit shrink is commonly estimated as offset height times shrink per inch for the selected bend angle. A 6 inch offset at 30 deg uses about 1/4 inch shrink per inch, so the shrink allowance is about 1.5 inches before field verification. Use this chart to decide when to add shrink back to the first mark and when the calculator already included the total allowance.

Shrink allowance by bend angle

Shrink allowance by bend angle
Bend angle	Shrink per inch	Shrink for 4 in offset	Shrink for 8 in offset
10 deg	1/16 in	0.25 in	0.50 in
15 deg	1/8 in	0.50 in	1.00 in
22.5 deg	3/16 in	0.75 in	1.50 in
30 deg	1/4 in	1.00 in	2.00 in
45 deg	3/8 in	1.50 in	3.00 in
60 deg	1/2 in	2.00 in	4.00 in

Where shrink belongs in the layout

Where shrink belongs in the layout
Layout type	Offset value to use	Watch for
Two-bend offset	Measured offset height	Fixed endpoint may need shrink added back
3-point saddle	Obstruction height	Center mark must stay tied to obstruction center
4-point saddle	Each offset pair	Do not add shrink twice if calculator reports total
Rolling offset	True diagonal offset	Do not use only the vertical or horizontal leg
Kick bend	Kick movement or calculator result	Take-up and box entry may matter more than shrink

Shrink chart to calculator handoff

Shrink chart to calculator handoff
Search or worksheet need	Use this chart for	Open the calculator when
Conduit shrink chart	Selecting the shrink-per-inch row for a known bend angle	Offset height, true offset, or saddle geometry must produce a saved allowance
Offset bend shrink	Checking whether shrink affects the first mark on a fixed-end run	Mark spacing and shrink need to be recalculated together after angle changes
Saddle bend shrink	Documenting whether each pair or the whole saddle already includes shrink	3-point or 4-point saddle marks must stay tied to obstruction center and width
Rolling offset shrink	Confirming that true offset, not one leg, controls the shrink allowance	Horizontal and vertical movement need one diagonal true-offset result

Formula basis

Shrink allowance = offset height x shrink per inch. Rolling offset shrink uses true offset. Paired layouts may already include both offsets.

Offset height is the rise, drop, saddle height, kick movement, or true diagonal offset used by the calculator.
Shrink per inch is selected from the bend angle used for the offset or saddle.
Total shrink is the planning allowance added back to keep a finished endpoint aligned.
True offset is used for rolling offsets where horizontal and vertical movement happen together.

Worked examples

6 inch offset at 30 degreesShrink allowance = 6 x 1/4 = 1.5 inches. Record that value beside mark spacing before deciding whether the first mark moves back.

Rolling offset with 8 inch true offset at 22.5 degreesShrink allowance = 8 x 3/16 = 1.5 inches. The true offset is the diagonal result, not just the rise or the side movement.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

The chart uses common field shrink allowances for planning and calculator documentation.
Actual shrink can vary with bender shoe geometry, conduit material, conduit size, bending technique, and how the measurement reference is held.
The worksheet should show whether shrink was already included in a paired saddle, rolling offset, or calculator total.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this as an estimating and layout record, then verify final alignment with the actual field bend, supports, and project requirements.

How to use this chart

1Start from calculator geometryUse offset height, saddle height, kick distance, or rolling true offset returned by the calculator.

2Match the selected angleChoose the shrink-per-inch row that matches the bend angle used in the calculator result.

3Record how shrink was appliedNote whether shrink was added to the first mark, held as a reference note, or already included in a total calculator output.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Record input geometryDocument offset, true offset, or obstruction height so shrink can be traced back to the calculator input.
Record angle rowWrite bend angle, shrink-per-inch value, and computed allowance next to the mark-spacing result.
Record field adjustmentAfter test fitting, write measured correction so the final conduit layout does not depend on memory.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Adding shrink twice when the calculator already reports total shrink for a paired saddle or paired offset.
Ignoring shrink on a fixed endpoint run, which can leave the finished conduit short of the intended landing point.
Using vertical offset instead of true diagonal offset on a rolling offset layout.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Is shrink the same as distance between bends?

No. Distance between bends is mark spacing. Shrink is the amount the finished run effectively shortens through the bend geometry.

Why does a rolling offset use true offset?

A rolling offset moves in two directions, so shrink follows the diagonal true offset instead of only the horizontal or vertical leg.

When should shrink be added back?

Add it back when a fixed endpoint must land at a box, coupling, support, or obstruction reference and the calculator has not already included that allowance.

When should I use a calculator instead of the shrink chart?

Use the calculator when the selected angle changes, the layout is rolling or paired, or the worksheet must show exact spacing and shrink from the same geometry.