Bending Reference
Conduit Bend Radius and Developed Length
The centerline bend radius a standard EMT hand bender makes, by size, and the developed length of a bend it produces, from the same verified profiles the calculator and 3D renderer use.
Bender Centerline Radius by EMT Size
Standard EMT hand benders (Ideal, Klein, Greenlee) each sweep one fixed centerline radius per conduit size. That radius is what take-up, gain, and mark spacing are all derived from. The tube outer diameter and wall come from ANSI C80.3 and UL 797.
| Conduit Size | Centerline Radius | Take-Up | Gain (90°) |
|---|---|---|---|
| 1/2" EMT | 4" | 5" | 1.72" |
| 3/4" EMT | 4.5" | 6" | 1.93" |
| 1" EMT | 5.75" | 8" | 2.47" |
| 1-1/4" EMT | 7.25" | 11" | 3.11" |
Bender Radius vs NEC Minimum Bend Radius
These are two different numbers, and mixing them up is common:
- Bender centerline radius (this page) is the fixed radius your hand bender physically makes, 4.5" for 3/4" EMT. It is what field marks and cut lengths come from, and what a finished EMT bend actually measures.
- NEC minimum bending radius is a separate code limit (NEC Chapter 9, Table 2) that keeps a bend from being tight enough to damage the conductors inside. It answers a different question and is not the same value. This page does not restate the NEC table.
For a standard EMT field bend, the bender radius above is the radius you get, because the bender makes only that one radius per size.
Developed Length of a Bend
The developed length of a single bend is the length of conduit that runs through the curve itself, measured along the centerline:
It scales straight with both the radius and the angle. The table below is the developed length, in inches, for each standard EMT bender radius across common bend angles.
| Size (Radius) | 10° | 22.5° | 30° | 45° | 60° | 90° |
|---|---|---|---|---|---|---|
| 1/2" (4") | 0.70 | 1.57 | 2.09 | 3.14 | 4.19 | 6.28 |
| 3/4" (4.5") | 0.79 | 1.77 | 2.36 | 3.53 | 4.71 | 7.07 |
| 1" (5.75") | 1.00 | 2.26 | 3.01 | 4.52 | 6.02 | 9.03 |
| 1-1/4" (7.25") | 1.27 | 2.85 | 3.80 | 5.69 | 7.59 | 11.39 |
Worked Exam Problems
The two developed-length questions that show up most on apprentice exams, worked from the formula above. Every answer is computed from the values the problem gives, nothing memorized.
Problem 1. What is the developed length for a 15° bend if the centerline radius is 25"? (a large-radius or factory bend, the classic exam setup)
Step 1: convert the angle to radians. 15 × π ÷ 180 = 0.2618 radians.
Step 2: multiply by the radius. 25 × 0.2618 = 6.54 inches.
Answer: the developed length is 6.54". The same formula works for any radius, which is why a tight bender radius develops far less length than a wide factory sweep at the same angle.
Problem 2. What is the formula for the developed length of a 90° bend, and what is it on a 3/4" EMT bender?
Step 1: the formula. A 90 is a quarter circle, so developed length = radius × (π ÷ 2) = radius × 1.5708.
Step 2: put in the 3/4" radius. 4.5 × 1.5708 = 7.07 inches.
Answer: developed length = radius × π/2, which is 7.07" for 3/4" EMT. The developed-length chart above gives every size: 6.28″ for 1/2", 7.07″ for 3/4", 9.03″ for 1", 11.39″ for 1-1/4".
Frequently Asked Questions
What is the bend radius of 3/4 inch EMT?
A standard 3/4 inch EMT hand bender makes a fixed centerline bend radius of 4.5 inches. That is the radius the bender shoe sweeps, and it is what the take-up, gain, and mark spacing all come from. By EMT size the bender centerline radius is 4 inches for 1/2 inch, 4.5 inches for 3/4 inch, 5.75 inches for 1 inch, and 7.25 inches for 1-1/4 inch. This is the bender radius, not the NEC minimum bend radius, which is a separate limit.
How do you calculate the developed length of a bend?
The developed length of a single bend is the length of conduit that travels through the curve: developed length = centerline radius x bend angle in radians, which is the same as (angle / 360) x 2 x pi x radius. For a 15 degree bend at a 25 inch centerline radius, developed length = 25 x (15 x pi / 180) = 6.54 inches. On a standard 3/4 inch EMT bender (4.5 inch radius) a 90 degree bend has a developed length of 7.07 inches.
Is the bender radius the same as the NEC minimum bend radius?
No. The bender radius is the fixed centerline radius your hand bender actually produces, and it is what field bend marks and cut lengths are figured from. The NEC sets a separate minimum bending radius for raceways (NEC Chapter 9, Table 2) so a bend never damages the conductors inside. They are different values that answer different questions. This page publishes the bender radius, which is what a standard EMT hand bend physically is; it does not restate the NEC table.
Does the bend radius change with conduit size?
Yes. A larger conduit uses a larger bender, so the centerline radius grows with size: 4 inches for 1/2 inch EMT, 4.5 inches for 3/4 inch, 5.75 inches for 1 inch, and 7.25 inches for 1-1/4 inch. Because developed length is radius times angle, a bigger radius also means a longer developed length for the same angle, which is why larger conduit saves more material (more gain) on a 90.
What is the developed length of a 90 degree bend?
For a 90 degree bend, developed length = radius x (pi / 2), a quarter of the full circle. On standard EMT benders that is 6.28 inches for 1/2 inch (4 inch radius), 7.07 inches for 3/4 inch (4.5 inch radius), 9.03 inches for 1 inch (5.75 inch radius), and 11.39 inches for 1-1/4 inch (7.25 inch radius). Developed length is the arc through the bend itself; to size a whole piece with 90s you subtract gain from the summed legs instead.
What is the developed length for a 15 degree bend if the centerline radius is 25 inches?
The developed length is 6.54 inches. Developed length is the conduit that runs through the curve, and it equals the centerline radius times the bend angle in radians: 25 x (15 x pi / 180) = 6.54 inches. Only the radius and angle the problem gives are used, so the same formula answers any radius, including a large-radius factory bend.
What is the formula for the developed length of a 90 degree bend?
Developed length = centerline radius times (pi / 2). A 90 degree bend is a quarter of a full circle, so its arc is the radius times pi/2 (1.5708 radians). On a standard 3/4 inch EMT bender the centerline radius is 4.5 inches, so the developed length is 4.5 x 1.5708 = 7.07 inches. The developed length chart above gives the value for every EMT size.
More Bending References
Conduit Bending Calculator
Calculate marks for all 7 bend types and see each bend as an interactive 3D rendering or flat diagram, from verified bender profiles.
Conduit Gain Chart
The material a 90 saves versus a square corner, and how to size a whole bent piece.
90° Deduction Chart
Take-up, deduct, radius, and gain for 1/2" through 1-1/4" EMT.
Offset Multiplier Chart
Multipliers and shrink per inch for 10° through 60° offset bends.