Parallel Offset Calculator
By Andrew ·
Quick answer
Parallel offsets keep a bank of conduits evenly spaced. Every conduit gets the same offset, but each next conduit's marks move further from the end by shift per conduit = center-to-center spacing × tan(angle ÷ 2), which is spacing × the shrink per inch. At 45° and 3" centers the shift is 1 1/4". Number the conduits from the side the offset moves toward.
Calculator
- Results
- Distance between bends
- 8"
- Move each next conduit’s marks by
- 9/16" (0.54")
- Last conduit’s marks move by
- 1 1/16" (1.07")
- Shrink of each conduit
- 1 1/16" (1.07")
Worked out the textbook way, from the bend angle alone. BendMate also uses your bender’s radius, deduct and shoe.
Why the marks shift
Around a bend, the conduit on the outside has further to go than the one inside it. If every conduit were marked alike, the bank would pinch together at one bend and spread at the other. Moving each next conduit’s marks along by a fixed shift keeps the gap the same all the way through.
shift = center-to-center spacing × tan(angle ÷ 2)The shift depends only on spacing and angle. It is the same for every size of bender, because it comes from the shape of the bank and not the shoe.
Worked example: four conduits at 3" centers
- Spacing, center to center
- 3"
- Offset height
- 4"
- Angle
- 45°
- Marks apart, each conduit
- 4" × 1.414 = 5 11/16"
- Shift per conduit
- 3" × 0.414 = about 1 1/4"
| Conduit | Both marks move by |
|---|---|
| 1 | Reference |
| 2 | 1 1/4" |
| 3 | 2 1/2" |
| 4 | 3 3/4" |
Steps for a bank
- Number the conduits starting from the side the offset moves toward. Conduit 1 sits on the inside of the first bend.
- Bend conduit 1 as an ordinary offset.
- For each next conduit, move both marks the shift further from the end and bend the same offset.
- Bend every conduit with the hook facing the same end, and keep the ends squared up when you install them.
Shift for common spacings
| Spacing | 22.5° | 30° | 45° |
|---|---|---|---|
| 2" | 3/8" | 9/16" | 13/16" |
| 3" | 5/8" | 13/16" | 1 1/4" |
| 4" | 13/16" | 1 1/16" | 1 5/8" |
| 6" | 1 3/16" | 1 5/8" | 2 1/2" |
Mistakes that spoil a bank
- Numbering the conduits from the wrong side, which pinches the bank instead of holding it.
- Marking from ends that are not lined up.
- Shifting by the spacing alone and forgetting to multiply by tan(angle ÷ 2).
- Changing the angle partway through the bank.
The offset for each conduit is still worked out for your bender, so in BendMate the same math accounts for your bender’s radius and deduct, with the shift laid on top.
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
How do you bend parallel offsets?
Bend the first conduit as an ordinary offset, then move both marks of each next conduit further from the end by spacing × tan(angle ÷ 2) and bend the same offset. Keep the hook facing the same end.
What is the shift per conduit at 30 degrees?
0.268" per inch of spacing, which is about 1/4" per inch. For conduits at 2" centers it is 9/16".
Does the shift depend on conduit size?
Only through the spacing. The shift comes from the center-to-center distance and the angle, so a bigger conduit changes it just by widening the spacing.
Which conduit do you bend first?
Conduit 1, the one on the inside of the first bend, which is on the side the offset moves toward. Its marks are the base, and every other conduit shifts away from them.