Bending Calculator
Segmented 90 Calculator
A 90 bent as equal shallow shots to a large centerline radius: the developed length of the sweep, the spacing between marks, the first mark and the angle of each shot, with every shot checked against the bend radius for the size.
The Method, Stated by Geometry
A segmented 90 spreads one 90 degree turn across many shallow bends of one angle so the finished sweep follows a radius far larger than the bender's shoe. The conduit that travels through a quarter circle of centerline radius R is R × π ÷ 2 long; dividing that developed length into equal spaces and bending each space's center by 90 ÷ shots lays out a polygon whose corners sit on that arc. Put the first mark half a space past the start of the bend, so the polygon's first side is centered on the tangent point, and every later mark one space farther. The marks are the bends: each is centered in the shoe and bent to the shot angle.
- Where the marks are measured from: the start of the bend, half a space before the first mark. It sits the drawn sweep's own radius back from where the two legs' centerlines would meet, a little under the target because the marks lay out a polygon (23.86" for the 24" example in six shots); the calculator prints that distance. The pipe is still straight for a short way past that point: it is a mark datum, not where the first arc begins.
- What the shoe adds: each shot is a short arc at the bender's own NEC Chapter 9, Table 2 radius, and that arc needs conduit on both sides of its mark. When the marks are closer than the two arcs need, the calculator refuses and names the smallest radius that works at that shot count and the fewest shots that work at that radius (more always fit).
- What the sweep actually draws: a polygon with rounded corners, not a perfect arc. The calculator prints the closest and farthest the drawn centerline sits from the sweep's center, and the largest round object centered on the sweep that the pipe wall clears.
- Shot count: 2 to 36. One shot is a 90 stub, which has its own calculator.
A 24" Radius in 1/2" EMT, by Shot Count
Every row is run through the calculator. The developed length is the same 37.7" in every row; the shots divide it. The last column is how far the drawn centerline actually sits from the sweep's center, closest to farthest.
| Shots | Each Shot | Mark Spacing | First Mark | Drawn Radius |
|---|---|---|---|---|
| 2 | 45° | 18.85" | 9.42" | 22.75" to 24.3" |
| 3 | 30° | 12.57" | 6.28" | 23.46" to 24.14" |
| 4 | 22.5° | 9.42" | 4.71" | 23.7" to 24.09" |
| 6 | 15° | 6.28" | 3.14" | 23.85" to 24.03" |
| 8 | 11.25° | 4.71" | 2.36" | 23.91" to 24.01" |
| 12 | 7.5° | 3.14" | 1.57" | 23.95" to 24.01" |
| 18 | 5° | 2.09" | 1.05" | 23.93" to 24" |
| 24 | 3.75° | 1.57" | 0.79" | 23.98" to 24" |
Smallest Radius That Fits, by Size and Shot Count
The target radius has to be a little larger than the shoe's own radius, and the margin above it shrinks as the shots multiply, so more shots always fit where fewer did. Each cell is the calculator's own re-run figure: the smallest target radius, to the sixteenth, at which every shot's arc still fits between its neighbours.
| EMT Size | Shoe Radius | 2 shots | 4 shots | 8 shots | 12 shots | 24 shots | 36 shots |
|---|---|---|---|---|---|---|---|
| 1/2" | 4" | 4-1/4" | 4-1/16" | 4-1/16" | 4-1/16" | 4-1/16" | 4-1/16" |
| 3/4" | 4.5" | 4-3/4" | 4-9/16" | 4-9/16" | 4-9/16" | 4-9/16" | 4-9/16" |
| 1" | 5.75" | 6-1/8" | 5-7/8" | 5-13/16" | 5-13/16" | 5-13/16" | 5-13/16" |
| 1-1/4" | 7.25" | 7-11/16" | 7-3/8" | 7-5/16" | 7-5/16" | 7-5/16" | 7-5/16" |
Worked Example: 24" Radius, 6 Shots, 1/2" EMT
Given: a run has to sweep around a 90 on a 24" centerline radius and you will make it in six shots.
Step 1: Developed length. 24 × π ÷ 2 = 37.7" of conduit goes through the sweep.
Step 2: Shot angle and spacing. 90 ÷ 6 = 15° per shot; 37.7 ÷ 6 = 6.28" between marks.
Step 3: The marks. Find the start of the bend, 23.86" back from where the two legs' centerlines would meet, and measure from it: 3.14", 9.42", 15.71", 21.99", 28.27", 34.56".
Result: six 15° bends whose drawn centerline runs 23.85" to 24.03" from the sweep's center, clearing a round object of up to 23.5" radius centered on it.
Frequently Asked Questions
How do you lay out a segmented 90?
Pick the centerline radius the sweep should follow and how many shots (equal shallow bends) you will make. Developed length = radius x pi / 2, so a 24 inch radius sweeps 37.7 inches of conduit. Divide that by the shot count for the mark spacing (6.28 inches in 6 shots), put the first mark half a space past the start of the bend (3.14 inches), and bend every mark to 90 divided by the shot count (15 degrees each). The start of the bend sits the drawn sweep's own radius back from where the two legs' centerlines would meet (23.86 inches for the 24 inch, 6 shot example in 1/2 inch EMT), a little under the target because the marks lay out a polygon, and the calculator prints that figure.
What angle is each shot?
The total turn divided by the number of shots: 90 in 6 shots is 15 degrees each, 90 in 12 shots is 7.5 degrees each, 90 in 18 shots is 5 degrees each. The apprentice exam calls this a concentric bend and asks the same division.
Why does the calculator refuse a small radius?
Every shot is bent in the bender's shoe, whose own centerline radius is fixed by the size (4 inches for 1/2 inch EMT, from NEC Chapter 9, Table 2). Each shot's arc takes up conduit on both sides of its mark, and when the marks are closer together than the two arcs need, the shots run into each other. That happens whenever the target radius is not larger than the shoe's own radius by a margin that shrinks with more shots: 5.5 percent at 2 shots and 0.1 percent at 12. The refusal names the smallest radius that works at your shot count and the fewest shots that work at your radius (more always fit), both found by re-running the same check.
Does the finished sweep really follow the radius I enter?
Not exactly, and the calculator says by how much. The marks lay out a polygon of straight segments with a short arc at each shot, so the drawn centerline sits a little inside the entered radius between shots and a little outside it at each shot: for 24 inches in 6 shots on 1/2 inch EMT it runs 23.85 to 24.03 inches from the sweep's center. More shots bring the two figures together. The calculator also prints the largest round object centered on the sweep that the pipe wall clears.
Where does this method come from?
From geometry, stated on this page. None of the bender manuals this site holds (Greenlee, Gardner Bender, Klein) prints a segmented-bend table; Gardner Bender's guide names segment and concentric bending as things its bender does and gives no numbers. So there is no table to cite and no rounding to inherit: the developed length is the arc length of a quarter circle, the spacing divides it evenly, and the shot angle divides the 90 evenly.
More Bending References
Conduit Bending Calculator
Every bend type as an interactive 3D rendering or flat diagram, with verified bender profiles.
Bend Radius and Developed Length
The centerline bend radius by EMT size and the developed length of a bend at any angle.
Compound 90 Calculator
Two bends around an obstruction in the corner, with the clearance the drawn bend actually gives.
Apprentice Exam Answers
The concentric-bend question and the rest of the exam's conduit math, worked from the same engine.
90° Deduction Chart
Take-up, deduct, radius, and gain for 1/2" through 1-1/4" EMT.
Conduit Fill Calculator
Check NEC Chapter 9 fill compliance for any conduit and conductor combination.
New: run this inside your AI assistant
Prefer to just ask? Add this to Claude, free.
Connect Intry to Claude once, then just say “use Intry to…” to run the segmented 90 calculator from a plain-English question, on your phone, on the job. You get the number (computed live, not guessed), what it means, and the bender chart or geometry it was computed from and the NEC Chapter 9 Table 2 radius. Works on every Claude plan.