When making segment bends, the developed length of the bend, the number of segments (shots), and the spacing between each bend mark must all be determined before you start bending. These three variables work together: get one wrong, and the entire bend comes out misaligned. Segment bends are used when a standard bender can’t produce the large-radius curves needed for bigger conduit sizes, so the bend is built up from multiple smaller bends spaced evenly along the conduit.
The Three Core Variables
Every segment bend starts with three pieces of information you need to calculate in advance:
- Developed length: The total arc length of the bend, measured along the centerline of the conduit. This depends on the bend’s radius and the total degree of the bend you need.
- Number of segments (shots): How many individual small bends you’ll make to build up the full curve. More shots produce a smoother bend but take longer.
- Spacing between marks: The distance between each bend point on the conduit. This is calculated by dividing the developed length by the number of segments.
The degree of each individual shot also needs to be determined. You divide the total bend angle by the number of segments. For example, a 90-degree bend made with 9 shots means each shot is 10 degrees.
How to Calculate Developed Length
Developed length is the distance the conduit actually travels through the curved portion of the bend. You calculate it from the centerline radius (CLR) of the finished bend, not the inside or outside edge. The CLR varies depending on the conduit’s outside diameter, wall thickness, and the angle of the bend.
The simplest approach: calculate the circumference of a full circle using the centerline radius (2 × π × radius), then divide by 360 to get the length per degree. Multiply that per-degree value by your total bend angle, and you have your developed length. For a 90-degree bend with a 24-inch centerline radius, the full circle circumference would be about 150.8 inches. Dividing by 360 gives roughly 0.419 inches per degree. Multiply by 90, and the developed length is about 37.7 inches.
Calculating Mark Spacing
Once you have the developed length, the spacing formula is straightforward:
Mark Spacing = Developed Length ÷ Number of Segments
Using the example above, a 37.7-inch developed length with 9 segments gives you roughly 4.19 inches between each mark on the conduit. You measure and mark these intervals along the conduit before placing it in the bender. Accuracy here matters a lot. Even small measurement errors compound across multiple shots, pulling the finished bend off target.
The number of segments you choose is partly a judgment call. More segments create a smoother, more gradual curve that looks cleaner and pulls wire more easily. Fewer segments save time but produce a more angular bend. For large conduit sizes, electricians commonly use anywhere from 5 to 15 shots depending on the radius and conduit diameter.
Finding the Center of the Bend
Locating the exact center of your total bend on the conduit is critical for positioning. The traditional method involves making a test bend and using straight edges to find where the two straight sections of conduit would intersect if extended through the curve. You place a straight edge along the inside of the conduit before the bend, draw a line through the curve, then do the same from the other side. Where those two lines cross is the center of the bend.
A faster approach used with some bending tools: mark a reference point on the conduit (typically 6 inches from one end), measure and mark all your segment spacing from that reference, then transfer those marks directly onto the bender shoe. This eliminates the trial-and-error of the traditional method and lets you work from a single unbent piece of conduit.
Minimum Bending Radius Requirements
The radius you choose for a segment bend isn’t entirely up to you. The National Electrical Code sets minimum bending radius requirements to prevent damage to the conduit and the conductors inside it. For most cable types, the radius of the inner edge of any bend must be at least five times the diameter of the cable.
A recent update in the 2026 NEC clarified how to measure this for flat cables like nonmetallic-sheathed (NM) cable. When bending a flat cable on its flat side, you use the minor (smaller) diameter dimension to calculate the minimum radius. For all other bending orientations, the major (larger) dimension applies. This same rule now extends uniformly to SE, USE, and UF cable types, so the bending radius calculation is consistent across similar flat cable styles.
For conduit specifically, minimum bend radius tables are published by manufacturers and vary by conduit type (EMT, rigid, PVC) and trade size. Staying above the minimum prevents kinking, cracking, and restricted wire-pulling paths inside the conduit.
Putting It All Together
Before you pick up a bender, your preparation checklist looks like this: determine the total angle of the bend you need, select an appropriate centerline radius that meets code minimums, calculate the developed length from that radius and angle, decide on the number of shots, divide the developed length by the number of shots to get your mark spacing, and then carefully measure and mark the conduit. Each shot gets bent to the same degree (total angle divided by number of segments), and the marks are evenly spaced along the conduit.
The most common mistakes happen before the bender is ever used. Forgetting to calculate from the centerline radius instead of the inside or outside edge throws off the developed length. Using the wrong conduit diameter in your radius calculation produces a bend that doesn’t fit the intended pathway. And inconsistent mark spacing, even by fractions of an inch, results in a bend that twists or spirals instead of curving in a single plane. Taking the time to determine all your variables accurately on paper is what separates a clean segment bend from one that has to be scrapped and redone.