Conduit offset (S-bend) calculator
Enter the offset and the bend angle to get the distance between bend marks, shrink, horizontal run and the pipe length needed for an offset bend. Pick EMT or RMC with NEC bend radii, Japanese JIS conduit, or Custom to enter the bend radius of your own bender. Works in mm or inches.
日本語版: 電線管S字曲げ計算ツール
Choose units, conduit & size
Units
Region / standard
Conduit type
Enter the offset
Results
Pipe length of the S-bend section
Two bend arcs + the straight diagonal run (varies with bend radius)
Two bend arcs + the straight diagonal run (varies with bend radius)
250mm
Distance between bends
(marking distance, center to center)
(marking distance, center to center)
200mm
Arc length of one bend
(R × angle)
(R × angle)
51mm
Horizontal width (1→2)
footprint of the S-bend
footprint of the S-bend
226mm
Shrink
(length lost versus a straight run)
(length lost versus a straight run)
27mm
Bend angle
30.0°
Multiplier
(1 ÷ sin angle)
(1 ÷ sin angle)
2.00×
Reference minimum bend radius (field bending)
-mm
This tool only helps with dimension calculation. Final decisions must follow the project specification, the applicable local code and your bender's instructions. Check the pipe cut length and conduit fill separately.
Diagram
How to read the diagram
Red dot = bend center: the marking position. Line the bender's arrow up with it.
Green 1 and 2 = start and end of the bent section: the pipe length between them is the S-bend length shown above.
Distance between bends = length along the pipe centerline from one red dot to the other (the marking dimension). It does not depend on pipe size.
S-bend length = pipe length from 1 to 2: two bend arcs plus the straight diagonal. Larger radius means a longer pipe.
Red dot = bend center: the marking position. Line the bender's arrow up with it.
Green 1 and 2 = start and end of the bent section: the pipe length between them is the S-bend length shown above.
Distance between bends = length along the pipe centerline from one red dot to the other (the marking dimension). It does not depend on pipe size.
S-bend length = pipe length from 1 to 2: two bend arcs plus the straight diagonal. Larger radius means a longer pipe.
Glossary
- Offset bend (S-bend)
- Two opposite bends in the same pipe that shift its axis sideways while keeping it parallel. Used to get around beams, other pipes or boxes.
- Offset
- The distance you want to shift the pipe (the height of the S).
- Bend angle
- How far the diagonal section is tilted from the straight run. 15°, 22.5°, 30°, 45° and 60° are common. A smaller angle needs more pipe but makes pulling cable easier.
- Distance between bends (center to center)
- The distance along the diagonal from the center of the first bend to the center of the second. This is the dimension you mark on the pipe. It depends only on the offset and the angle, not on pipe size.
- Arc length of one bend
- The length of pipe inside one bend: arc = R × angle (in radians), measured along the centerline. A larger radius gives a longer arc. Example: at 30°, R = 98 mm gives 51 mm and R = 324 mm gives 170 mm.
- Pipe length of the S-bend section
- The actual pipe consumed: two arcs + the straight diagonal. Use it as a guide for the cut length.
- Horizontal run
- How far the pipe advances along the straight direction through the S-bend.
- Shrink (take-up)
- The difference between the distance between bends and the horizontal run. It is the length you lose compared with a straight pipe, important when matching distances to fixed boxes or equipment. This tool gives it for the ideal geometry; your bender's own take-up marks may differ.
- Multiplier
- The factor that turns the offset into the distance between bends: 1 ÷ sin(angle) (2.00 at 30°, 1.414 at 45°). Handy for working it out in your head on site.
- Minimum offset for a single S-bend
- With a large radius and a small angle, the two bends collide below an offset of 2R(1 − cosθ). This does not mean the offset is impossible: split it into two or more S-bends, use a larger angle, a smaller pipe, or a factory-made bend.
- NEC Table 2 bend radius (United States)
- The U.S. National Electrical Code (NFPA 70) sets a minimum bend radius by trade size in Chapter 9, Table 2, measured to the centerline of the bend. The table has one column for one-shot and full-shoe benders and one for other bends. The values here are from the 2017 edition. Which column applies to a given conduit type, and which edition your jurisdiction has adopted, must be checked against your own code book.
- Reference minimum bend radius (Japan)
- For the JIS conduits in this tool, the radius shown is 6 × inner diameter, taken from Japan's wiring rules (JEAC 8001). The rule exists to keep enough bend radius for the cable inside, not as a physical limit of the pipe, so factory-made bends can be tighter.
- Bender / hickey
- The tool used to bend conduit. A hickey is a hand tool for small sizes; hydraulic benders are used for large sizes.
- Normal bend (factory-made elbow)
- A factory-made elbow. For large conduit, on-site offsets are often hard to make, so a route is usually built from factory bends whose radius is given in the manufacturer's catalog.
Quick multiplier table (per 1 of offset)
| Angle | Between bends 1 ÷ sinθ |
Run 1 ÷ tanθ |
Shrink between − run |
|---|---|---|---|
| 15° | 3.864 | 3.732 | 0.132 |
| 22.5° | 2.613 | 2.414 | 0.199 |
| 30° | 2.000 | 1.732 | 0.268 |
| 45° | 1.414 | 1.000 | 0.414 |
| 60° | 1.155 | 0.577 | 0.577 |
How to use it: multiply your offset by the table value. For a 100 mm offset at 30°: between bends = 100 × 2.00 = 200 mm, run = 100 × 1.73 = 173 mm, shrink = 100 × 0.27 = 27 mm. These ideal values ignore the bend radius.