Bending Technique
Back-to-Back 90 Bends
The star-point (teardrop) field method for two 90s on one stick, plus the from-the-end marks by EMT size and why the second mark subtracts the gain. Bend two parallel stubs exactly the distance apart you need, with no math at the pipe.
The Star-Point Method (No Math at the Pipe)
Every major bender maker (Ideal, Klein, Greenlee) casts a second symbol into the shoe for exactly this bend: the star point, also called the teardrop or tear. It sits back from the arrow so you can reference the back of a finished bend instead of the end of the conduit. That is what lets you make a back-to-back with a tape and no arithmetic:
- Bend the first 90 as a normal stub. Mark at stub height minus the take-up, line the mark up with the arrow, and pull to 90 degrees.
- Flip the conduit end for end. The first stub now points up on the far side, and the finished bend gives you a hard back to measure from.
- Measure the back-to-back distance from the back of the first bend. Hook your tape on the back of the first 90 and mark the distance you want between the two stubs.
- Align the star point with that mark and bend. Line the teardrop symbol, not the arrow, up with your mark and pull the second 90. The backs of the two bends now sit exactly the measured distance apart.
The star point exists because the second bend is referenced from the back of the first bend, not the end of the pipe. Using the arrow there would put the bend off by one bend's worth of geometry (the gain). The calculator below gives the same bend as from-the-end marks if you would rather lay both out before bending.
Back-to-Back 90 Calculator
Enter the stub height, the distance between the two 90s, and your conduit size for both marks from the end, the total gain, and the developed length to cut, with an SVG or 3D diagram.
Star-Point Marks by EMT Size
If you lay both marks out from the end before bending, the first mark is stub height minus take-up and the second (star) mark is first stub plus distance minus the gain. Below is a 18" stub with the two 90s 24" apart, for each EMT size, with the total developed length to cut.
| EMT Size | First Mark | Star Mark (from end) | Gain × 2 | Cut Length |
|---|---|---|---|---|
| 1/2" EMT | 13.00" | 39.58" | 4.84" | 55.16" |
| 3/4" EMT | 12.00" | 39.15" | 5.70" | 54.30" |
| 1" EMT | 10.00" | 38.37" | 7.26" | 52.74" |
| 1-1/4" EMT | 7.00" | 37.38" | 9.24" | 50.76" |
First mark = stub − take-up. Star mark = stub + distance − gain. Cut length = both stubs + distance − gain for each 90. Verify take-up and gain against your own bender with a test bend before cutting a full stick.
Worked Example: 12" Stubs, 24" Apart in 3/4" EMT
Given: Two parallel 12" stubs with their backs 24" apart, in 3/4" EMT (take-up 6", gain 2.85").
Step 1: First mark. 12 − 6 = 6.00" from the end. Bend the first stub to 90 at that mark.
Step 2: Field method. Flip the conduit, hook your tape on the back of the first bend, mark 24" out, align the star point, and bend the second 90.
Step 2 (from the end instead): the star mark is 12 + 24 − 2.85 = 33.15" from the same end as the first mark.
Step 3: Cut length. Both stubs plus the run, minus the gain for each 90: 12 + 24 + 12 − 5.70 = 42.30" of conduit.
Result: A squared-off U with two 12" stubs whose backs are exactly 24" apart, cut from a 42.30" piece.
Why the Marks Subtract the Gain
A 90-degree bend follows a curved radius, so the finished path is shorter than two straight legs meeting at a square corner. That saved length is the gain, and it is why both the star mark and the cut length subtract it. A back-to-back has two 90s, so the cut length subtracts the gain twice.
One subtlety trips people up: there are two gain numbers for the same conduit, and they differ by exactly one conduit outside diameter. The pure arc savings is measured on the pipe's centerline; the field gain is measured to the outside corner, where your tape actually reaches, one full OD farther out. Field layouts and this page use the field gain, so the marks reconcile with a tape.
| EMT Size | Gain per 90 (field) | Pure Arc Savings | Back-to-Back Total (2 × 90) |
|---|---|---|---|
| 1/2" EMT | 2.42" | 1.72" | 4.84" |
| 3/4" EMT | 2.85" | 1.93" | 5.70" |
| 1" EMT | 3.63" | 2.47" | 7.26" |
| 1-1/4" EMT | 4.62" | 3.11" | 9.24" |
The field gain is the pure arc savings plus one conduit outside diameter, so it is always the larger of the two numbers. Field charts and this page use it because it is what a tape reaches. See the conduit gain chart for the size-by-size breakdown.
Frequently Asked Questions
How do you bend a back-to-back 90?
Bend the first 90 as a normal stub: mark the conduit at the stub height minus the take-up and pull to 90 degrees. Then flip the conduit end for end, hook your tape on the back of the first bend, and measure the distance you want between the two 90s to a second mark. Align the star (teardrop) symbol on the bender shoe with that second mark, not the arrow, and bend the second 90. The backs of the two bends now sit exactly that distance apart, with no arithmetic in the field.
Where does the second mark go on a back-to-back 90?
In the field you do not calculate it: you measure the back-to-back distance from the back of the first bend and align the star point. If you would rather lay both marks out from the end of the conduit, the second mark equals the first stub height plus the distance between the stubs minus the gain for the second bend. For two 12-inch stubs 24 inches apart in 3/4-inch EMT, that is 12 + 24 - 2.85 = 33.15 inches from the end. The gain is subtracted because your legs are measured to the outside corner, where a tape reaches.
What is the star point (teardrop) on a conduit bender?
The star point, also called the teardrop or the tear, is a second reference symbol cast into the bender shoe, set back from the arrow. It marks where to line up the second bend of a back-to-back so the finished bend lands the correct distance from the first one when you measure from the back of the first bend. Using the arrow instead of the star would place the bend one bend's worth of geometry off. The star point is what makes back-to-back layout a zero-math measurement in the field.
Why do you subtract the gain on a back-to-back 90?
Each 90-degree bend follows a curved radius, so the finished path is shorter than two straight legs meeting at a square corner. That saved length is the gain, and you lose it once per bend. When you lay a back-to-back out from the end of the conduit, the second mark subtracts one gain; when you size the whole piece for cutting, you subtract the gain for both 90s. For 3/4-inch EMT the gain is 2.85 inches per 90, so a back-to-back subtracts 5.70 inches total. Forgetting the gain is the number-one back-to-back error and leaves the conduit too long between the stubs.
What is a back-to-back 90 used for?
A back-to-back 90 is two 90-degree bends on one piece of conduit with both stubs pointing the same way, forming a squared-off U. Electricians use it to stub up into two parallel boxes or panels a set distance apart, to run up one wall and down another, or to make a matched pair of vertical drops on a rack. The whole point is that the two stubs land parallel and exactly the specified distance apart, which is why the second bend references the back of the first.
What distance do the two 90s end up apart?
The distance you measure is between the backs of the two 90-degree bends, which is the length of the flat run between the two stubs. When you measure from the back of the first bend to the star mark and bend, the outside corners of the two bends end up exactly that distance apart. Both stubs rise from the ends, so the finished U is the back-to-back distance wide at the bottom with a stub at each end.
More Bending References
Conduit Bending Calculator
All 7 bend types as an interactive 3D rendering or flat diagram, with verified bender profiles.
90° Deduction Chart
Take-up, deduct, radius, and gain for 1/2" through 1-1/4" EMT, with stub-up marks.
Conduit Gain Chart
Field gain and the pure arc savings by size, and the developed-length formula.
Kick 90 Calculator
Kick marks, travel, and shrink per inch of kick for stub-and-kick combos.
Printable Cheat Sheet
Every bending constant on one page. Print, save the PDF, or download the image.
How Many Bends Are Allowed?
The NEC 360° rule: max four 90s between pull points, and why offsets and saddles count.