What changes at 30 degrees
With 30 degree fittings, the travel is the true offset times 2.000. The run is the true offset times 1.732. Every inch of true offset costs 0.268 inch of length in a bent conduit run (shrink).
- Travel = true offset x 2.000
- Run = true offset x 1.732
- Shrink per inch of offset = 0.268 in
Why electricians like 30 degrees
The multiplier is exactly 2. The distance between the two bends is twice the true offset. You can do it in your head: a true offset of 15 inches means the marks are 30 inches apart.
Shrink is about 1/4 inch for each inch of offset, so a 15 inch true offset loses about 4 inches of length.
Using 30 degrees with pipe
A 30 degree pipe fitting is also called a 1/12 bend in drain, waste and vent work. It is less common than the 45. This site has no catalog take-off for it, so type the take-off of your own fitting in Pipe mode.
Rise and roll pairs at 30 degrees
These pairs give a whole number for the true offset, so you can check your own math against them.
| Rise | Roll | True offset | Travel at 30° | Run at 30° |
|---|---|---|---|---|
| 3" | 4" | 5.00" | 10" (10.00) | 8 11/16" (8.66) |
| 6" | 8" | 10.00" | 20" (20.00) | 17 5/16" (17.32) |
| 5" | 12" | 13.00" | 26" (26.00) | 22 1/2" (22.52) |
| 12" | 9" | 15.00" | 30" (30.00) | 26" (25.98) |
| 8" | 15" | 17.00" | 34" (34.00) | 29 7/16" (29.44) |
| 24" | 7" | 25.00" | 50" (50.00) | 43 5/16" (43.30) |
Compare with the other angles
The offset is the same. Only the fitting angle changes. A smaller angle makes a longer travel and a longer run.
| Angle | Multiplier | Travel | Run | Shrink |
|---|---|---|---|---|
| 22.5° | 2.613 | 39 3/16" (39.20) | 36 3/16" (36.21) | 3" (2.98) |
| 30° | 2.000 | 30" (30.00) | 26" (25.98) | 4" (4.02) |
| 45° | 1.414 | 21 3/16" (21.21) | 15" (15.00) | 6 3/16" (6.21) |
| 60° | 1.155 | 17 5/16" (17.32) | 8 11/16" (8.66) | 8 11/16" (8.66) |
Questions
What is the multiplier for 30 degrees?
It is 2.000, because the sine of 30 degrees is 0.5.
How far apart are the bends for a 12 inch rise and 9 inch roll?
The true offset is 15 inches, so the bends are 30" apart.
Can I use a 30 degree bend in a rolling offset?
Yes. A rolling offset can use any bend angle. Both bends use the same angle.