How the bend math works
Every offset is a right triangle. The offset depth is the side opposite the bend angle, and the conduit between the two bends is the hypotenuse. So the distance between marks is depth × csc θ, which is the multiplier, and the run gets shorter by depth × (csc θ − cot θ), which is the shrink.
| Angle | Multiplier | Shrink per inch |
|---|---|---|
| 10° | 5.759 | 0.087 in |
| 22.5° | 2.613 | 0.199 in |
| 30° | 2.000 | 0.268 in |
| 45° | 1.414 | 0.414 in |
| 60° | 1.155 | 0.577 in |
Worked examples
- 6" offset with 30° bends. Marks 12.00 in (12") apart; the run shrinks 1.61 in (1 5/8").
- 12" stub-up in ½" EMT. The bender's take-up is 5 in, so mark 7" from the end and line up the arrow. Take-up for the other hand-bender sizes: ½" 5 in, ¾" 6 in, 1" 8 in, 1¼" 11 in.
- 3-point saddle over a 2" pipe, 45° centre. Outer bends of 22.5° each, outer marks 5 1/4" either side of the centre mark, shrink 3/8".
- 4-point saddle over a 4" obstacle with 30° bends. Two offsets, each with marks 8" apart; total shrink 2 1/8".
- Rolling offset, 4" rise and 3" roll, 30° bends. The true offset is 5", so the marks are 10" apart.
Step-by-step guides: Offset multipliers and shrink chart and 3 point saddle bend: layout, multiplier and shrink.
Where these numbers come from
The geometry is the trigonometry taught in Benfield's Conduit Bending and tabulated in Ugly's Electrical References, not an NEC calculation. Stub take-up is the figure on standard hand benders. For 1½" and larger, take-up depends on the bender (hydraulic and electric benders each have their own), so the calculator leaves it to you instead of guessing.
Worked examples on this page are computed by the same engine as the Voltkit app. The page cites NEC 2023 sections but doesn't reproduce NFPA text or tables; use your copy of the code for the exact wording.