By Blissom · Updated 2026-10-23
Layout values: check them against your own bender, on scrap first.
The triangle behind every bend
Picture an offset from the side. The conduit between the two bends is the long side (hypotenuse) of a right triangle. The short vertical side is the offset depth, the angle at the first bend is the bend angle θ, and the horizontal side is how far along the run the offset travels.
Offsets
csc θ (cosecant, 1 ÷ sin θ) is the "multiplier". Bender guides use convenient field values close to it: 10° = 5.76 (used as 6), 22.5° = 2.61 (2.6), 30° = 2.00, 45° = 1.41 (1.4), 60° = 1.15 (1.2). They are field approximations rather than plain roundings, and the bending chart lists both.
Shrink
Shrink is how much shorter the run gets because the conduit travels diagonally for part of it: the hypotenuse minus the horizontal side. The identity csc θ − cot θ = tan(θ/2) gives the per-inch values: 10° = 0.087 (sticker 1/16"), 22.5° = 0.199 (3/16"), 30° = 0.268 (1/4"), 45° = 0.414 (3/8"), 60° = 0.577 (1/2").
The field shrink values are smaller than the ideal ones, and the gap grows with depth: 10" at 45° gives 4-1/8" of shrink by the ideal geometry and 3-3/4" by the field rule. A real bend on a shoe differs from both, so check deep offsets against your bender.
3-point saddles
With a 45° center and 22.5° outer bends, csc 22.5° = 2.61. For 3-point saddles bender guides print 2.5 instead (offsets at 22.5° use 2.6), so the field outer marks sit about 0.11" closer per inch of depth than the sharp-corner geometry, and tan 11.25° = 0.199 becomes the 3/16" per inch center shift. For a 60° center with 30° outer bends the guides give 2.0 and 1/4". See the 3-point saddle calculator.
4-point saddles
Two offsets of the saddle depth. Marks 2 and 3 define the central section. The finished level section must take the obstruction width plus the clearance on both sides, and because the bends occupy part of the marked spacing, a mark-to-mark distance equal to width plus clearance does not give that same finished straight length. Allow for the shoe radius and the marking reference, and verify clearance with a test bend. Each side uses the offset formulas, and the total shrink is twice the offset shrink. See the 4-point saddle calculator.
90° stubs: take-up
The take-up is a property of the shoe: the distance from the arrow to the back of the finished 90. Klein's guides give 5", 6", 8" and 11" for 1/2" to 1-1/4" EMT; other makers can differ. It depends on the shoe's radius and where the arrow is cast on it, which is why every size has its own number. Chart: bender deduct chart.
Gain and developed length
Gain is the conduit a bend saves compared with legs that meet at a sharp corner. If you measure the legs to the outside of a 90 (as stub heights and back-to-back distances are), the gain is one conduit diameter larger.
Kicks
A kick is half an offset: one bend, the same triangle. When you know where the end has to land, solve the angle from the rise and the run.
Rolling offsets
Then treat the true offset as a normal offset depth. See the rolling offset calculator.
Parallel offsets
In a rack of conduits bent at the same angle, each conduit's marks move this much farther along than the one inside it, so the bends nest and the spacing stays close to even through the offset.
Segmented bends
Developed length ÷ shots spaces the shots evenly along the arc, the method segment-bender manuals use; the tangent-polygon spacing 2R × tan(θ_shot ÷ 2) is slightly longer. See the segmented 90 calculator for both.
Worked example: the formulas on one saddle
A saddle 3" deep is needed over a pipe whose center is 40" from the end of the conduit. With a 45° center bend and the field values:
- Center shift: 3 × 3/16" = 9/16". Add it to the measured 40" to the obstruction center: 40 + 9/16 = 40-9/16" from the conduit end.
- Outer marks: 3 × 2.5 = 7-1/2" either side: 33-1/16" and 48-1/16".
- Estimated total shrink of the run: 2 × 9/16" = 1-1/8". Bends: 45° + 22.5° + 22.5° = 90° toward the 360° limit.
When the shoe radius matters
All of the offset formulas above assume sharp corners. A real bend is an arc on the shoe's radius, which saves a little conduit at each bend (the gain for that angle). On a 1/2" shoe with a 4-5/8" radius the gain is under 1/16" per bend at 30° or less, about 0.2" at 45° and about 0.5" at 60°; larger shoes gain more, and on tight saddles the arcs can even overlap. The mark spacing corrected for the shoe is:
This only holds when the two bends do not overlap: two equal bends on radius R need a depth of at least 2R × (1 − cos θ), about 1.24" at 30° and 2.71" at 45° on a 4-5/8" radius shoe. The same correction applies to shrink, twice (once per bend). The Conduit Bending Calculator app does this for the shoe you pick; the web calculators on this site use the field values from bender guides.
Sources: NEC 2023 358.24 and Chapter 9, Table 2; Klein Tools Conduit Bender Guide (stub take-up, offset multipliers and shrink, saddles). Method.
Questions electricians ask
What is the formula for a conduit offset?
Distance between bends = depth × csc θ (1 ÷ sin θ). Shrink = depth × tan(θ ÷ 2). At 30°, csc = 2 and tan 15° = 0.268, so a 6" offset has marks 12" apart and shrinks about 1-5/8" by the ideal geometry (1-1/2" by the 1/4"-per-inch field rule).
Why is the 30 degree multiplier 2?
Because sin 30° = 0.5, and the multiplier is 1 ÷ sin θ. The conduit between the bends is the hypotenuse of a right triangle whose opposite side is the offset depth.
What is the formula for gain?
For a 90° bend on centerline radius R, gain = 2R − πR/2 ≈ 0.429 × R. For any angle θ, gain = 2R·tan(θ/2) − R·θ (θ in radians). For legs measured to the outside of the bend, add one conduit diameter for a 90.
Exact math without doing the math
- Exact trigonometry, corrected for the radius of your shoe
- Or the sticker numbers your crew uses, one switch
- Any angle, including odd ones solved from what you measured
- Every step shown with the numbers filled in
Android only. There is no iPhone version yet; the free calculators on this site work on any phone.
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