30 degree conduit offset: multiplier and shrink
By Andrew ·
Quick answer
The multiplier for a 30 degree offset is 2.000, so the bends go twice the offset height apart. Shrink is 0.268" per inch of height, which the trade rounds to 1/4". A 6" offset at 30° has the marks 12" apart and shrinks about 1 5/8", where the rule of thumb gives 1 1/2".
30° offset marks
| Offset height | Distance between bends | Shrink |
|---|---|---|
| 1" | 2" | 1/4" |
| 2" | 4" | 9/16" |
| 3" | 6" | 13/16" |
| 4" | 8" | 1 1/16" |
| 5" | 10" | 1 5/16" |
| 6" | 12" | 1 5/8" |
| 7" | 14" | 1 7/8" |
| 8" | 16" | 2 1/8" |
| 9" | 18" | 2 7/16" |
| 10" | 20" | 2 11/16" |
| 12" | 24" | 3 3/16" |
| 15" | 30" | 4" |
| 18" | 36" | 4 13/16" |
| 24" | 48" | 6 7/16" |
Why 30 degrees is the default
Thirty degrees is the angle most offsets are bent at, for three reasons. The bends are easy to pull and easy to see on any hand bender. The multiplier is exactly 2, so the spacing is arithmetic you can do in your head. And it covers the sizes of offset that come up most, from an inch or two off a box to eight inches around a beam, without the long run of a shallow angle or the extra shrink of a steep one.
- Measure the offset height, center to center, and double it. That is the distance between the bends: 10" for a 5" offset.
- Take a quarter of an inch for each inch of height as the shrink. The exact figure is 0.268", a touch more, so for tall offsets add a little.
- Put the first mark on the arrow, bend to 30°, roll half a turn, and bend the second mark to 30°.
Rounded numbers against exact numbers
Both rules of thumb for 30° are about as good as they get: the multiplier is exact and the quarter-inch shrink is within about 7% of the true figure. Still, the gap grows with the height of the offset. Where it matters, such as when you measure from the end and the conduit has to land a set distance from a box, use the exact shrink.
| Offset height | Between bends | Shrink | Shrink (rule) |
|---|---|---|---|
| 2" | 4" | 9/16" | 1/2" |
| 4" | 8" | 1 1/16" | 1" |
| 6" | 12" | 1 5/8" | 1 1/2" |
| 8" | 16" | 2 1/8" | 2" |
| 10" | 20" | 2 11/16" | 2 1/2" |
| 12" | 24" | 3 3/16" | 3" |
A real shoe bends on a radius, so on a bender the spacing and shrink come out slightly smaller than the chart. BendMate allows for the radius of your own bender; the chart is the sharp-corner version.
When to leave 30 degrees
Thirty degrees runs out of room when the offset is tall and the space between the bend and the obstruction is short. Moving to 45° cuts the length you need for the same offset height by about 30%.
| Offset height | At 30° | At 45° | Length saved |
|---|---|---|---|
| 3" | 6" | 4 1/4" | 1 3/4" |
| 4" | 8" | 5 11/16" | 2 3/8" |
| 6" | 12" | 8 1/2" | 3 1/2" |
| 8" | 16" | 11 5/16" | 4 11/16" |
| 10" | 20" | 14 1/8" | 5 7/8" |
| 12" | 24" | 17" | 7 1/16" |
Get the marks for your bender
BendMate works this out from your bender’s radius and deduct, flags a bend that won’t work, and shows you every mark.
Common questions
What is the multiplier for a 30 degree offset?
2.000, so the distance between the bends is twice the offset height. A 7" offset needs 14" between bends.
How much does a 30 degree offset shrink?
0.268" per inch of height. The common rule of 1/4" per inch is slightly short: a 6" offset shrinks 1 5/8" but the rule gives 1 1/2".
Does every conduit bender have a 30 degree mark?
Most hand benders carry a 30° line or a notch on the head, and electric and mechanical benders have a degree scale. Confirm yours with a level on a test bend.
When should I use 45 degrees instead of 30?
When the offset is tall or the space is short. A 45° offset needs about 30% less length between bends than 30° does for the same height, at the cost of more shrink.