Conduit Bending Calculator: Offsets, Saddles and Shrink
A 4 in. offset bent at 30° puts the two marks 8″ apart and costs 1″ of shrink — add that to your measurement to the obstacle.
Calculator
Offset
8″
Total shrink
1″
Angle
30°
Distance between bends. Mark-to-mark on the conduit.
Method: at 30°, ×2 between marks and 1/4 in. of shrink per inch of offset.
How it’s calculated
Offset: marks = H × multiplier; shrink = H × shrink per inch
3-point saddle: center to each side mark = H × 2.5; shrink to the center mark = H × 3/16
4-point saddle: first to last mark = 2 × (H × multiplier) + L; shrink = 2 × H × shrink per inch
H
the offset, or the height of the obstacle, in inches
L
the flat length across the top of the obstacle, in inches
multiplier
6 at 10°, 2.6 at 22.5°, 2 at 30°, 1.414 at 45°, 1.155 at 60°
shrink per inch
1/16 in. at 10°, 3/16 in. at 22.5°, 1/4 in. at 30°, 3/8 in. at 45°, 1/2 in. at 60°
At 10°, 22.5° and 30° the multipliers are the figures bender makers print. At 45° and 60° this calculator, like the Electric Master app, uses 1.414 and 1.155, where bender heads print 1.4 and 1.2. The shrink figures are the ones benders print.
Results are shown to the nearest sixteenth of an inch, the way a tape reads; each figure is rounded on its own.
Assumptions
Bends made on a hand bender to the angle chosen. A bender that springs back, or a mark read off the wrong side of the arrow, moves the result more than any rounding here.
The offset is measured square to the run, centerline to centerline.
The 3-point saddle is always the 45° center with 22.5° sides; other combinations use other multipliers.
The 4-point saddle's inner marks are exactly the obstacle's length apart. Add any clearance you want to that length before you enter it.
Shrink is the length the offset takes out of the run. Working toward an obstacle, add it to the distance to the first mark; working away from one, it needs no correction.
No bender deduct is involved: offsets and saddles are placed by their marks, not by a stub height.
Worked examples
A 4-point saddle over a 4 in. × 12 in. duct
Two 22.5° offsets, one each side of the duct, with its 12 in. top between them.
Each offset: the 22.5° multiplier times the rise4 × 2.6= 10 3/8″ between the marks of one offset
The two inner marks sit the length of the duct apart; the outer marks one offset further out on each side:2 × 10.4 + 12= 32 13/16″ from the first mark to the last
Shrink, for both offsets2 × 4 × 3/16= 1 1/2″
Answer: Marks 10 3/8″, 12″, 10 3/8″ apart — 32 13/16″ overall, from the unrounded 10.4 in. — and 1 1/2″ of shrink.
Bender heads print 6, 2.6, 2, 1.4 and 1.2; this calculator uses 6, 2.6, 2, 1.414 and 1.155, as the Electric Master app does; trigonometry gives 10° 5.759, 22.5° 2.613, 30° 2.000, 45° 1.414, 60° 1.155. The gaps that show are at 10°, where 6 against 5.76 moves a 6 in. offset's marks by about 1 7/16″, and at 60°, where 1.2 against 1.155 moves a 10 in. offset's marks by about 7/16″.
Check: whether the other tool uses the printed bender figure, three decimals or trigonometry.
Chart shrink or sharp-corner shrink
Some tools compute shrink as if each bend were a sharp corner: 10° 0.087, 22.5° 0.199, 30° 0.268, 45° 0.414, 60° 0.577 in. per inch, against the chart's 1/16, 3/16, 1/4, 3/8, 1/2. A real bend has a radius and shrinks less than a sharp corner, so that figure is an upper bound, not a more exact one.
Check: which shrink the other tool used, and on a large offset trust a test bend.
A different 3-point saddle
Some saddles use a 60° center with 30° sides, which has its own multiplier and shrink. This one is the 45° and 22.5° saddle.
Check: the angles the other tool assumed.
Along the conduit or along the wall
The distance between marks is measured along the straight conduit before it is bent. A figure measured along the wall after bending is shorter.
Check: where the other figure was measured.
Questions
What is the multiplier for each offset angle?
6 at 10°, 2.6 at 22.5°, 2 at 30°, 1.414 at 45°, 1.155 at 60°. Multiply the offset by it to get the distance between the two bend marks.
How much shrink per inch of offset?
1/16 in. at 10°, 3/16 in. at 22.5°, 1/4 in. at 30°, 3/8 in. at 45°, 1/2 in. at 60°. A 4 in. offset at 30° shrinks the run by 1″.
Why doesn't my offset land where the marks said?
Usually the bend, not the arithmetic: springback that leaves the angle short, a mark read off the wrong side of the arrow, or the two bends not quite in one plane. The shrink figures are close to what a hand bender gives; on a large offset a test bend settles it.
How many degrees does each bend add toward the limit between pull points?
An offset is two bends, so 60° at 30° and 90° at 45°. A 3-point saddle is 90°, and a 4-point saddle at 22.5° is 90°. A run may carry no more than 360° between pull points.
Which angle should I use?
The smallest one that fits the space. A shallow angle costs less shrink and adds fewer degrees toward the limit between pull points, but it needs a longer straight run between the marks: a 10° offset needs 6 times its height, a 60° offset only 1.155 times.
Where do I measure the marks?
Along the conduit, before it is bent, from mark to mark. The offset itself is measured square to the run, from the conduit's centerline before the offset to its centerline after.
Written and maintained by Yusuf Can Samiloglu: MEP/HVAC design background, mechanical-engineering degree, not a licensed electrician.
How it’s checked: the calculation is the method of the Electric Master app, ported to the web and tested case by case against the app’s source code. The multipliers and shrink figures are bender makers’ and trade figures, not NEC values, compared with at least two published bender guides; the NEC 2023 references cover only the bend radius and the 360° limit.
: The 3-point saddle row is the shrink to the center mark, and the parallel-offset row is the start stagger per conduit; a length that is not a finite number up to 10,000 in. is refused.
: First version. Offsets at 10°, 22.5°, 30°, 45° and 60°, the shrink each one costs, the 3-point saddle’s fixed 45° geometry and the 4-point saddle across a flat obstacle, with the multipliers and shrink figures of the Electric Master app.