Shrinkage
Conduit shrinkage chart
Shrink is the run an offset takes out of a straight stick. Ignore it and the far end lands short of the box. This conduit shrinkage chart is the lookup for that loss, angle by angle, using the same constants as the WattsCalc offset card.
WattsCalc already explains these constants on the conduit bending shrink chart. This page is the chart for the “conduit shrinkage chart” query. The figures match. Use either page as a lookup, then enter height and angle on the conduit offset calculator when you want marks and shrink for a specific height. Diagrams live on the conduit bending cheat sheet.
How to read a row
For an offset:
Distance between marks = offset height × multiplier
Shrink (add to the run) = offset height × shrink per inch of height
The field card rounds to the nearest 1/16 inch. Bend radius is not included. Shrink on the offset follows the angle, not the trade size. Constants follow Klein Tools bending charts. WattsCalc is not affiliated with Klein Tools, Ideal, or Greenlee. Verify on your shoe before a production bend.
Shrinkage chart
| Angle | Multiplier | Shrink per inch of height |
|---|---|---|
| 10° | 5.76 | 1/16" |
| 15° | 3.86 | 1/8" |
| 22.5° | 2.61 | 3/16" |
| 30° | 2.00 | 1/4" |
| 45° | 1.41 | 3/8" |
| 60° | 1.15 | 1/2" |
The multiplier column is here because a layout needs both numbers. The spacing-only table, and the comparisons that go with it, are on the EMT offset multiplier chart.
Worked example: 6″ offset at 30°
The homepage offset opens at 6 inches of height and 30°. Multiplier 2.00. Shrink 1/4″ per inch of height.
- Distance between marks: 6 × 2.00 = 12″.
- Shrink: 6 × 1/4″ = 1 1/2″.
Both products are exact, so the 1/16-inch round does not move them. If the obstruction is 6″, plan an extra 1 1/2″ of conduit in the straight run. The 30° multiplier is 2.00, the cosecant of 30°, which is why a 6″ offset is 12″ between marks on the live card.
A fraction height uses the same 30° row. A 6 1/2″ offset is 6.5 × 2.00 = 13″ between marks and 6.5 × 1/4″ = 1 5/8″ of shrink. Both land on a 1/16-inch mark. Confirm that pair on the offset calculator before you mark the stick.
A second row: 5″ at 22.5°
Shrink per inch at 22.5° is 3/16″. Total shrink is 5 × 3/16″ = 15/16″. Mark spacing is 5 × 2.61 = 13.05″ before the tool rounds to the nearest 1/16 inch. The 15/16″ is the figure crews skip when they mark spacing and forget shrink.
Shallow angles and steep angles
A 10° offset shrinks the least per inch, 1/16″, and needs the longest marks, multiplier 5.76. A 60° offset uses multiplier 1.15 and shrinks 1/2″ per inch of height. Pick the angle the box allows. The smallest shrink is not automatically the right row.
EMT, IMC, and rigid
The offset constants are angle math. The homepage kicker covers EMT, IMC, and rigid, and the product ships an offline PWA. Typical 90° stub-up take-up is a different table: 1/2″ EMT → 5″, 3/4″ EMT → 6″, 1″ EMT → 8″. Those take-up figures are typical. Verify on your shoe. Do not use the offset shrink column as stub take-up, and do not use stub take-up as offset shrink. Rigid and IMC shoes can differ; treat this chart as the math reference and confirm marks on scrap.
Chained offsets need each leg’s shrink added. One card is one offset. Estimates only: verify against your bender and local electrical code before you cut.
FAQ
What is conduit shrinkage?
It is the extra run an offset consumes compared with a straight path between the same ends.
Does offset shrink change with EMT size?
On the offset card, shrink per inch follows the angle. Confirm the bend on scrap for your shoe.
Why can a field bend miss the chart?
Shoe wear, a different bender, and bend radius (not included in the math) can move the real marks.
What is the 30° row?
Multiplier 2.00 and shrink 1/4″ per inch of height. A 6″ offset is 12″ between marks and 1 1/2″ of shrink.
Open the conduit bending calculator
Results are estimates for reference only. Always verify measurements against your bender and local electrical code before cutting or bending conduit.
