Calculadora de offset de conduit
To bend an offset, enter the height you need to clear (the rise) and the angle of your two bends. The distance between the marks is the rise times the offset multiplier for that angle; the shrink is how much the run pulls in, which you add to your measurement so the far end lands where you want it. The "Do it" list under the number is the three lines to follow at the bender, and "Show the working" puts your own rise through the formula step by step.
On the bender
The five moves for an offset, with the marks in them. The calculator above has already done the arithmetic; this is the order I do it in at the tool.
- Measure. The rise is centre-of-pipe to centre-of-pipe — where the run is now to where it has to end up — not edge to edge. Then measure from the end of the stick to where the jog has to start; that is the layout measurement.
- Mark. Mark 1 goes at the layout measurement itself — the pipe between the end and mark 1 is dead straight and loses nothing, so the shrink does not move it. Mark 2 goes the between-marks distance (rise × multiplier) further along. Draw both lines all the way round the pipe so you can see them from either side of the shoe.
- Line up. Bender on the floor, arrow on mark 1, hook toward the far end. Foot on the pedal, hands on the handle.
- Bend. Steady pull to the angle line, a touch past for springback, let off. Slide the pipe forward without lifting it out of the groove, roll it a half turn so the second bend goes the other way, arrow on mark 2, and pull the same angle. Sight down the pipe before the second pull: both bends must be in one plane or you get a dog leg.
- Add the shrink to the length. The jog eats the shrink out of the finished run, so everything past mark 2 pulls back by that much. Add it to the overall measurement — the cut length, or the distance to the far box — before you cut. Moving mark 1 does not buy it back; a stick that is already too short needs a longer stick or a coupling.
- Check. Lay it on the floor. Both flats should touch without rocking and the far leg should sit exactly the rise above the near one. Rocking means the bends are twisted; short means the shrink was left off the overall length.
Worked examples
A 6" (152 mm) box offset at 30°
You need a 6" (152 mm) offset at 30° to clear a box. The multiplier for 30° is exactly 2, so your two marks go 12" (305 mm) apart (6 × 2). The shrink for 30° is 0.268 × the rise, so 6 × 0.268 ≈ 1 5/8" (41 mm). Mark 1 goes where the jog has to start, the second mark 12" (305 mm) past it, and you bend the same angle at each. The 1 5/8" (41 mm) is what the jog takes out of the finished length, so it goes on the overall run — cut the stick that much longer, or the far end lands that much short.
A 150 mm offset at 30°, metric job
Same bend on a metric drawing: the run has to step 5 7/8" (150 mm) to clear a cable tray. At 30° the marks go 150 × 2 = 11 13/16" (300 mm) apart, and the shrink is 150 × 0.268 = 40.2 → 1 9/16" (40 mm). The jog covers 10 1/4" (260 mm) of flat run (150 × √3 = 259.8), so check you have that much clear under the tray. Add the 1 9/16" (40 mm) to the overall length before you cut; mark 1 stays where the jog starts.
14" (356 mm) over a duct at 45°, in a short run
A duct sits 14" (356 mm) proud of the wall your run is following, and the run has only 3' 0" (914 mm) before the next box. At 45° the multiplier is 1.414, so the marks go 14 × 1.414 = 19.8 → 19 13/16" (503 mm) apart, and the shrink is 14 × 0.414 = 5.8 → 5 13/16" (147 mm). That is where shrink stops being a rounding error: nearly 6" (152 mm) of the run vanishes into the bends, and if you had laid out from the box without adding it the far end would land in the middle of the duct. Add the 5 13/16" (147 mm) to the length of the stick, not to mark 1. Then check the jog itself fits: at 45° a 14" (356 mm) rise needs 14" (356 mm) of clear flat run underneath it, and there are 36" (914 mm) to the next box, so it does — with 22" (559 mm) left for the tails either side.
Typed in feet and inches
A rack has to come up 1' 3 1/2" (394 mm) to clear a beam. Type
1' 3 1/2" straight into the rise field — the calculator reads
it as 15 1/2" (394 mm). At 30° the marks go 15 1/2 × 2 =
31" (787 mm) apart and the shrink is 15 1/2 × 0.268 = 4.15
→ 4 1/8" (105 mm). Marks that far apart make a long,
shallow jog that is easy to pull but needs 26 7/8" (682 mm) of clear
run under it (15 1/2 × √3 = 26.85); if the beam is close to a wall, switch the chip to 45° and
see what the calculator does to the between-marks distance. In metric, type
millimetres the same way: 394 is the same rise.
The same 6" (152 mm) offset at 22.5°, 30° and 45°
The most common question at the bender is which angle to use. Here is one offset three ways. "Run" is the flat distance the jog covers — the room you need under it.
| Ángulo | Entre marcas | Run under the jog | Encogimiento | Which means |
|---|---|---|---|---|
| 22.5° | 15 11/16" (398 mm) | 14 1/2" (368 mm) | 1 3/16" (30 mm) | Long and easy to pull; needs 14 1/2" (368 mm) of clear run. |
| 30° | 12" (305 mm) | 10 3/8" (264 mm) | 1 5/8" (41 mm) | The everyday choice: ×2 in your head, moderate shrink. |
| 45° | 8 1/2" (216 mm) | 6" (152 mm) | 2 1/2" (63 mm) | Compact, but the shrink is nearly half the rise. Use when the run is short. |
A shallow angle spreads the jog out and shrinks less, so it is easier to pull true and kinder on the wire pull. A steep angle keeps the offset short but eats the run. Most people settle on 30° for anything with room and 45° when there is not, and never touch 60° unless the obstruction is right on top of the box.
Try one — an offset
Work it on paper, then type the marks. A sixteenth either way counts — that is as close as a tape reads. Two millimetres either way counts.
Loading a bend…
Escriba pulgadas como 12, 1 5/8 o 1' 3 1/2".
What went wrong
The three ways an offset goes bad, what you see, and the fix.
Dog leg
What you see: the pipe rocks on the floor, or the far end lands off to one side though the rise is right.
Why: the second bend was not in the same plane as the first — the pipe rolled a few degrees between the two pulls.
Fix: sight down the pipe before the second pull and line the first bend up with the shoe. A pencil line down the top of the pipe from mark 1 to mark 2 makes the roll visible.
Lands short
What you see: the rise is right, the bends are clean, and the end stops short of the fitting by an inch or two (25–50 mm).
Why: the stick was cut to the flat distance, and the two bends pulled the far end back by the shrink.
Fix: add the shrink to the overall length before you cut — not to mark 1, which sits on straight pipe and never moves. On a big rise at 45° it is nearly half the rise, so it is not a rounding error.
Far leg not level
What you see: the run climbs or dips after the offset instead of coming back parallel.
Why: the two bends are not the same angle — one pulled to the line, the other a little past it, or springback took more off one than the other.
Fix: pull both to the same line and both the same touch past it; check the first with a level before the second. If the pipe is a hard one, an extra degree on each pull is normal.
The formula
The distance between the marks is the rise divided by the sine of the angle:
between marks = rise ÷ sin θ
shrink = rise × (1 ÷ sin θ − 1 ÷ tan θ)
The offset is the vertical leg of a right triangle and the pipe between the marks is the hypotenuse, so the hypotenuse is the rise over sin θ. Shrink is the difference between that hypotenuse and its horizontal run. That is all the math there is — no table, no chart, just the triangle, drawn and derived on the formulas page.
Exact multiplier vs. the shop rule
Shop multipliers are rounded for mental math. They are fine for small offsets; the rounding starts to matter on large offsets and tight runs, where 1/8" (3.2 mm) of drift moves the far end noticeably. The shrink column is a ratio: multiply it by the rise, in inches or millimetres. The shop-shrink column is the exact figure rounded up to the next sixteenth, not down: a shrink figure that is always low lands the run short, which is the one failure worth avoiding. Rounded up it errs long, and pipe you can trim.
| Ángulo | Multiplier | Shop rule | Shrink × rise | Shop shrink (in per in) |
|---|---|---|---|---|
| 10° | 5.759 | 6 | 0.087 | 1/8 |
| 22.5° | 2.613 | 2.6 | 0.199 | 1/4 |
| 30° | 2.000 | 2 | 0.268 | 5/16 |
| 45° | 1.414 | 1.4 | 0.414 | 7/16 |
| 60° | 1.155 | 1.15 | 0.577 | 5/8 |
Which bender these numbers assume — and how to adjust
The geometry belongs to the angle, not the tool. What the tool changes — its reference marks, its take-up and gain, its springback — is yours to read off the shoe or prove on scrap, never a table here (the four test bends). For this bend:
For an offset both marks go on the arrow, which on a hand bender is the start of the bend, and both bends are pulled to the same degree line on the shoe. Nothing else about the bender enters the numbers: the multiplier and the shrink are pure angle. If your bender has no degree scale, or you doubt it, put a level or a protractor on the pipe after the first bend and read the real angle — then use "Other angle" above so the second mark matches what you actually pulled.
Preguntas
- Why is my offset coming out short?
- Almost always shrink. Bending an offset pulls the far end back toward the bends, so the run is shorter than the flat length you measured. Add the shrink figure to your original measurement before you make the first mark.
- What angle should I use for a small offset?
- A smaller angle gives a longer, gentler jog and less shrink, which is easier to pull off cleanly in a tight space. 22.5° and 30° cover most box and panel offsets; 45° is for clearing something deep in a short run.
- Does shrink apply to saddles too?
- Yes, but the amount is different. A three-point saddle uses the shrink of its outer bend angle, applied to the depth. Use the saddle calculator rather than the offset shrink for those.
- Is the multiplier the same for every conduit size?
- The geometric multiplier is. It comes only from the angle, so 30° is always ×2 whether you are bending half-inch EMT or two-inch rigid. Take-up and gain change with the bender and the pipe; the offset multiplier does not.
- Which way do I turn the pipe between the two bends?
- End for end, so the second bend goes the opposite way and brings the run back level. Keep both bends in the same plane — sight down the pipe before the second pull. If the two bends are rotated relative to each other the far end rolls off to one side.