Conduit bending formulas
By Andrew ·
Quick answer
Offset spacing is the offset height ÷ sin(angle), or height × the multiplier: 2.000 at 30° and 1.414 at 45°. Shrink is height × tan(angle ÷ 2). A 90 is marked at the stub length minus the deduct. A rolling offset uses √(rise² + roll²). Each formula below has a worked example.
The formulas
- Offset: distance between bends
height × multiplierThe multiplier is 1 ÷ sin(angle). - Offset: shrink
height × tan(angle ÷ 2)How much shorter the conduit ends up. - 90° stub-up: mark
stub length − deductMeasured from the stub end to your bender’s arrow. - 3-point saddle: outer marks
height × 2.5 each side of the centerFor a 22.5° / 45° / 22.5° saddle. - Rolling offset: true offset
√(rise² + roll²)Then use it as the offset height. - Parallel offsets: shift
spacing × tan(angle ÷ 2)Move each next conduit’s marks by this much. - Sweep or arc: conduit used
radius × angle in radiansDeveloped length of a bend.
Offsets: spacing and shrink
between bends = height ÷ sin(angle) = height × multipliershrink = height × tan(angle ÷ 2)- Offset height
- 6"
- Angle
- 45°
- Multiplier
- 1.414
- Between bends
- 8 1/2"
- Shrink
- 2 1/2"
The multiplier is 1 ÷ sin(angle): 5.759 at 10°, 2.613 at 22.5°, 2.000 at 30° and 1.155 at 60°. The shrink per inch is tan(angle ÷ 2): 0.087" at 10°, 0.268" at 30° and 0.577" at 60°.
90 degree stub-ups
mark at = stub length − deductdeduct = start of bend + centerline radius + OD ÷ 2- Stub length
- 12"
- Deduct (most hand benders)
- 5"
- Mark at
- 7"
Saddles
center bend = 2 × outer bendcenter mark to outer mark = obstruction height ÷ sin(outer bend)- Obstruction height
- 3"
- Outer bends
- 22.5°
- Center mark to each outer mark
- 7 13/16"
- Total shrink
- 1 3/16"
Rolling, parallel and kicks
true offset = √(rise² + roll²)shift per conduit = spacing × tan(angle ÷ 2)kick distance = kick height ÷ sin(angle)- Rise
- 6"
- Roll
- 8"
- True offset
- 10"
- Between bends
- 20"
- Roll the bends off plumb
- 53.13°
These formulas treat every bend as a sharp corner. A real shoe bends on a radius, so the figures from your bender come out slightly smaller. For anything that has to land to the sixteenth, work it out from the bender’s own radius and deduct.
Reading the formulas
Every offset is a right triangle. The offset height is the side opposite the angle, the conduit between the bends is the long side, and the run along the original line is the side next to the angle. Sine, cosine and tangent link the three, and the multiplier you carry in your pocket is just 1 ÷ sin(angle) with the division done for you.
- Height first. Measure the offset height center to center, then pick the angle.
- Spacing before shrink. The distance between bends comes from the multiplier; shrink is a second, separate step.
- Mark from one end. Carry each bend’s shrink forward when a run has more than one bend.
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 formula for a conduit offset?
Distance between bends = offset height ÷ sin(angle), the same as height × multiplier. At 30° the multiplier is 2.000, so a 6" offset needs 12" between the bends.
What is the formula for shrink?
Shrink = offset height × tan(angle ÷ 2). At 30° that is 0.268" per inch, so a 6" offset shrinks 1 5/8".
What is the formula for marking a 90 degree stub-up?
Mark at = stub length − deduct, measured from the end of the conduit, with the mark lined up with the arrow on the bender.
Why do bender numbers differ from the formulas?
The formulas treat each bend as a sharp corner. A real shoe bends on a radius, which uses a little less conduit.