FabLayout

Conduit offset calculator

Enter the offset depth and the bend angle. You get the distance between marks, the shrink and a scale drawing of the bend.

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Enter your measurements

Offset

Pinch or scroll to zoom, drag to move. Double-tap to fit.

Export from the Truemark app

The PDF cut sheet with this drawing and your marks is made in Truemark. It works offline on site and keeps your jobs.

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Mark spacingMark spacing1212″″30°30°Offset heightOffset height66″″ShrinkShrink115588″″
Scale drawing

Distance between marks

12in

Exact geometry

Shrink
1 5/8 in
Multiplier
2.000
Bender chart multiplier
2.000

How to lay it out

  1. Measure the offset depth

    Measure from the face of the obstruction to where the conduit has to sit, centre to centre.

  2. Add the shrink to your measurement

    Measure to the obstruction and add the shrink shown here. That point is your first mark.

  3. Mark the second bend

    Measure back from the first mark by the distance between marks and make the second mark.

  4. Bend both marks to the same angle

    Bend at the first mark, roll the conduit 180° and bend at the second mark in the opposite direction.

Good to know

  • FabLayout runs the same code as Truemark; the result is exact geometry.
  • Source: Greenlee Textron, Site-Rite Hand Bender Instruction Manual, IM 1071 Rev 4, offset table, p. 5

Method and formula

An offset moves a run of conduit onto a new plane with two equal bends in opposite directions. Two numbers matter on the pipe: how far apart the bend marks are, and how much the run shortens.

  • Distance between marks = offset depth × cosecant of the bend angle (depth ÷ sin θ).
  • Shrink = offset depth × tan(θ ÷ 2). Add it to your measurement to the obstruction so the second bend lands where you need it.

Bender charts round the cosecant to a field multiplier: 6.0 for 10°, 2.6 for 22½°, 2.0 for 30°, 1.4 for 45° and 1.2 for 60° (Greenlee IM 1071 Rev 4, offset table, p. 5). This calculator uses the exact value and shows the chart multiplier next to it, so you can check against the one stamped on your own bender.

Worked example

Greenlee's manual, Example 2: a 10″ offset with 45° bends. By the chart, the marks are 10 × 1.4 = 14″ apart and the shrink is 10 × ⅜ = 3¾″. The exact geometry gives 14⅛″ between marks. The ⅛″ difference is the rounding in the 1.4 multiplier; on short offsets it disappears inside the bend, on long ones it adds up.

Questions

Why is the exact multiplier different from my bender chart?

The chart rounds the cosecant of the angle: 1.4 for 45° is really 1.414. On a 10″ offset that is ⅛″. Use one system for both numbers: chart multiplier with chart shrink, or exact with exact.

Which angle should I use?

Use the shallowest angle that fits. A 10° offset puts the marks six times the depth apart, which is easy to pull but needs room. 45° is compact but harder to pull wire through when several offsets are in one run.

Does shrink matter on short offsets?

Yes, when the offset has to land at a fixed point, such as a box or an obstruction. Without the shrink, the offset lands short by that amount.

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