Conduit shrink worksheet
Conduit Shrink Calculator
Calculate shrink allowance for a conduit offset so the layout can compensate for the shortening caused by the bends.
Calculate Offset Bend Shrink
Enter offset height and bend angle to calculate shrink allowance; a 6 in offset at 30 degrees uses about 1.5 in shrink.
Result
Shrink per inch
0.25 in/in
Shrink
1.50 in
Estimated layout allowance to compensate for offset shrink.
Result notes
Keep the entered values, assumptions, and result together when adding this calculation to job notes or submittal records. Final installation choices should align with the applicable code edition, equipment listing, manufacturer instructions, local amendments, and AHJ requirements.
Related calculators
Offset Bend Calculator
Field-chart geometry screen for bend spacing, shrinkage allowance, travel, and optional bend-mark layout.
Saddle Bend Calculator
Calculate 3-point and 4-point saddle bend marks for conduit runs over obstacles.
Segment Bend Calculator
Geometry screen for equal-angle segmented conduit bends with bend angle, chord step, and bend-mark stations.
Related charts
Conduit Shrink Chart
Use a conduit shrink chart to compare bend angle, offset height, true offset, shrink per inch, and layout allowance after a calculator result.
Offset Bend Multiplier Chart
Use offset multiplier chart: 15 deg = 3.9, 22.5 deg = 2.6, 30 deg = 2.0 and 45 deg = 1.414; a 4 in offset at 30 deg marks 8 in.
Segment Bend Layout Chart
Use a segment bend layout chart to document total angle, bend count, centerline radius, bend angle per mark, chord spacing, and field stations.
Related guides
Conduit Fill Guide | 4 #6 THHN = 38.1%
Use conduit fill calculator example: 4 #6 THHN in 3/4 EMT uses 38.1%; compare NEC 40% fill, conductor count and ampacity derating.
Conduit Fill Table | 3/4 EMT #12, #10 and #6
Use this conduit fill table: 3/4 EMT fits 16 #12, 10 #10, 5 #8, or 4 #6 THHN at 40%; compare EMT, RMC and PVC sizes.
Formula and field context
Calculate shrink allowance for a conduit offset so the layout can compensate for the shortening caused by the bends.
Formula context
Conduit Shrink Chart
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.
Formula
Shrink allowance = offset height x shrink per inch. Rolling offset shrink uses true offset. Paired layouts may already include both offsets.Variables to keep with the result
- 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.
Formula and variables
Offset shrink is an allowance used to compensate for the way a bent offset shortens the straight run. This worksheet uses common field shrink factors: 10 degrees = 1/16 in per inch of offset, 22.5 degrees = 3/16 in per inch, 30 degrees = 1/4 in per inch, 45 degrees = 3/8 in per inch, and 60 degrees = 1/2 in per inch. The formula is shrink = offset height x shrink factor.
Field example
A 6 in offset using 30 degree bends has a shrink factor of 1/4 in per inch. The estimated shrink is 6 x 1/4 = 1.5 in. That means the mark layout normally needs to account for about 1.5 in of shortening compared with a straight conduit run. A 6 in offset using 45 degree bends has an estimated shrink of 6 x 3/8 = 2.25 in.
Assumptions and layout limits
Shrink factors are practical layout references, not a substitute for the bender instructions. The final field result can vary with conduit trade size, bender shoe radius, hand bender versus mechanical bender, exact bend angle, and how the mark is aligned with the arrow or reference line. Use this output as a layout allowance and confirm it against a test bend when precision matters.
Common mistakes
Common mistakes include applying shrink in the wrong direction, using multiplier values as shrink factors, ignoring the selected bend angle, and forgetting that shrink is separate from mark spacing. Keep the offset height, bend angle, shrink factor, and calculated allowance together so the layout can be checked before the conduit is bent.