Cutting, layout and conduit
Conduit offset bend calculator: multipliers and shrink
An offset is two equal bends that move a run of conduit over by a set height. The angle you pick decides how far apart the bends are and how much shorter the conduit gets. Here are the numbers and where they come from.
Offset multipliers and shrink chart
The distance between the two bends is the offset height times the multiplier, which is 1 ÷ sin(angle). The shrink, how much shorter the run gets, is the offset height times tan(angle ÷ 2). Electricians round the shrink to the inch fractions in the last column.
| Angle | Multiplier | Shrink per inch | Field figure |
|---|---|---|---|
| 10° | 5.759 | 0.087 in | 1/16 in |
| 22.5° | 2.613 | 0.199 in | 3/16 in |
| 30° | 2.000 | 0.268 in | 1/4 in |
| 45° | 1.414 | 0.414 in | 3/8 in |
| 60° | 1.155 | 0.577 in | 1/2 in |
How do you calculate an offset bend?
Example. A 6 in offset at 30°: the bends are 6 × 2 = 12 in apart, and the shrink is 6 × 0.268 = 1.61 in, about 1 5/8 in (the rule of thumb, 1/4 in per inch, gives 1 1/2 in).
Example. A 4 in offset at 22.5°: the bends are 4 × 2.613 = 10.45 in apart, about 10 7/16 in, and the shrink is 4 × 0.199 = 0.80 in, about 13/16 in.
Which angle should I use?
Shallow angles pull wire more easily but need room: at 10° the bends of a 6 in offset are 34.6 in apart. Steep angles fit tight spaces but use up more of the bends allowed in a run: the US National Electrical Code allows 360° of bends between pull points.
How do you bend a three-point saddle?
A common three-point saddle uses a 45° bend in the middle and a 22.5° bend on each side. Put the outer marks 2 1/2 in from the center mark for every inch of obstruction height, and allow about 3/16 in of shrink per inch.
Example. A 2 in pipe to cross: the outer marks go 5 in either side of the center mark, and the run shrinks about 3/8 in.
How do you mark a stub-up?
For a 90° stub-up, subtract the bender's take-up from the stub height and mark that distance from the end of the conduit. Take-up depends on the bender and the conduit size, so read it off your bender's markings.
Example. A 12 in stub with a bender whose take-up is 5 in: mark at 12 − 5 = 7 in from the end.
Conduit bending in Clad
Clad's conduit tool does offsets at 10, 22.5, 30, 45 and 60°, three-point saddles and stub-ups. It works the multiplier and the shrink out from the angle itself, gives the marks from the end of the conduit when you give the first one, and warns when the bends are too close for most benders.