Rolled offset calculator
A rolled offset moves a run up and sideways at once. Enter how far it rises and how far it rolls across; the calculator gives the true offset (the real distance to bend for), the roll angle to rotate the pipe before you bend, and the distance between your two marks.
On the bender
A rolled offset is an ordinary offset bent with the pipe rotated. The calculator turns the rise and the roll into one true offset and an angle to turn the pipe; here is how those become marks.
- Measure. How far the run has to go up (the rise) and how far across (the roll), centre to centre. The calculator gives the true offset — the straight-line distance between where the run is and where it must end up — and the roll angle.
- Mark. Lay out exactly as for a plain offset of the true offset: mark 1 at the layout measurement (straight pipe before it, so the shrink does not move it), mark 2 the between-marks distance further on, and the shrink added to the overall length. Then draw a pencil line along the pipe, from mark 1 through mark 2, rotated from top-dead-centre by the roll angle — a protractor or a torpedo level held at the angle sets it.
- Line up. Arrow on mark 1 with the pencil line straight up through the centre of the shoe, so the bend leans by the roll angle.
- Bend. Pull the offset angle. Slide to mark 2, roll a half turn as for any offset, and centre the pencil line under the shoe again before the second pull — the roll has to be the same at both bends or the far end lands beside the target instead of on it.
- Check. Hold it against the job: the far end should sit the rise up and the roll across from the near end. If it is right in one direction and off in the other, the roll angle was wrong; if both are proportionally short, the shrink was left off.
Worked examples
Up 6, over 4, at 30°
Say the run has to rise 6" (152 mm) and move 4" (102 mm) sideways to meet the next box, bent at 30°. The true offset is √(6² + 4²) = 7.21 → 7 3/16" (183 mm), and the roll angle is atan(4 ÷ 6) = 33.7°. Roll the pipe to 33.7° off vertical, then bend that offset at 30°: the multiplier is 2, so the marks go 14 7/16" (366 mm) apart (7.21 × 2 = 14.42). Add the 30° shrink on the true offset — about 1 15/16" (49 mm) — to your measurement.
Up 300 mm, over 400 mm, metric job
On a metric job the run climbs 11 13/16" (300 mm) and shifts 15 3/4" (400 mm) across — a 3-4-5 in millimetres, so the true offset is 19 11/16" (500 mm). Roll angle atan(400 ÷ 300) ≈ 53.1° off vertical. At 30° the marks go 500 × 2 = 39 3/8" (1000 mm) apart, and the shrink is 500 × 0.268 = 134 → 5 1/4" (134 mm), added to the overall length.
Up 12, over 5 — a 5-12-13 you can do in your head
A run comes off a panel and has to climb 12" (305 mm) and shift 5" (127 mm) to the left to land on the next strut. That is a 5-12-13 triangle, so the true offset is 13" (330 mm) without a calculator. Roll angle is atan(5 ÷ 12) ≈ 22.6° — a bit past twenty degrees off vertical, leaning toward the side the run has to move. At 30° the marks go 13 × 2 = 26" (660 mm) apart and the shrink is 13 × 0.268 ≈ 3 1/2" (88 mm). Notice the shrink is worked on the 13, not the 12 — the pipe travels the diagonal, so the diagonal is what shrinks.
Up 3, over 4, at 22.5° — a small one across a joist
A 3-4-5: true offset 5" (127 mm), roll angle atan(4 ÷ 3) ≈ 53°, which is more sideways than up, as it should be when the roll is bigger than the rise. At 22.5° the multiplier is 2.613, so the marks go 5 × 2.613 = 13.07 → 13 1/16" (332 mm) apart and the shrink is 5 × 0.199 ≈ 1" (25 mm). Any rise-and-roll pair from the 3-4-5 family (6-8-10, 9-12-15) gives a whole-number true offset, and so does any other Pythagorean triple — 5-12-13 and 8-15-17 are their own, not multiples of 3-4-5. The drill below uses them.
Try one — a rolled 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
It rises but does not move over
What you see: the far end reaches the right height and is still the roll distance off to one side.
Why: the offset was bent to the rise instead of the true offset. A 12" (305 mm) offset cannot cover a 13" (330 mm) diagonal; it lands 1" (25 mm) short along the diagonal, and that shows up mostly as the missing sideways move.
Fix: always bend the hypotenuse. Rise and roll go in, true offset comes out, and the true offset is the only number the marks are worked from.
It leans the wrong way
What you see: the jog moves the run to the right when it needed to go left.
Why: the pipe was rolled the right amount in the wrong direction before the first bend. The roll angle has no sign of its own — you supply it by which way you turn the pipe.
Fix: put the pencil line on the pipe, hold it up against the job and turn it until the line leans toward where the run has to go. Then bend, and do not let it turn back.
The two bends fight each other
What you see: the offset does not lie flat on anything; the far end is twisted off the plane of the first fitting.
Why: the second bend was pulled at a different roll from the first. Both bends have to be in the same tilted plane, and the tilted plane is easy to lose when you flip the pipe end for end.
Fix: the pencil line again. After the flip, the line must still lean the same way relative to the shoe before you pull the second bend. Check it, then bend.
The formula
The rise and the roll are two legs of a right triangle; the true offset is the hypotenuse:
true offset = √(rise² + roll²) · roll angle = atan(roll ÷ rise)
Once you have the true offset, the rest is an ordinary offset:
between marks = true offset ÷ sin θ and the same shrink as any
offset, applied to the true offset. The roll angle only tells the pipe which
way to lean so the jog points where you need it.
Exact vs. the shop rule
The multiplier and shrink are the ordinary offset figures — they act on the true offset rather than on the rise. Rounded shop multipliers are fine for small jogs; on a long rolled offset the rounding drifts, and so does an eyeballed roll angle, so it is worth taking the true offset and the roll angle off the exact figures here.
| Ángulo | Multiplier | Shop rule | Shrink × true offset |
|---|---|---|---|
| 10° | 5.759 | 6 | 0.087 |
| 22.5° | 2.613 | 2.6 | 0.199 |
| 30° | 2.000 | 2 | 0.268 |
| 45° | 1.414 | 1.4 | 0.414 |
| 60° | 1.155 | 1.15 | 0.577 |
At a glance — true offsets that come out whole
Rise and roll pairs that form a Pythagorean triple give a whole-number true offset — the 3-4-5 family and its multiples, plus triples of their own like 5-12-13 and 8-15-17. The triples work in any unit — 300 / 400 / 500 mm is the same triangle as 3 / 4 / 5 in. If your job is close to one of these, it is a fast sanity check on the calculator's figure before you mark the pipe. The roll angle is the same for every pair in a row — it only depends on the shape of the triangle.
| Rise / roll (either way round, any unit) | Offset real | Roll angle, roll ÷ rise |
|---|---|---|
| 3 / 4, 6 / 8, 9 / 12, 12 / 16 | 5, 10, 15, 20 | 53.1° (or 36.9° swapped) |
| 5 / 12, 10 / 24 | 13, 26 | 67.4° (or 22.6° swapped) |
| 8 / 15 | 17 | 61.9° (or 28.1° swapped) |
| 7 / 24 | 25 | 73.7° (or 16.3° swapped) |
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:
The two marks go on the arrow like any offset. The bender-specific part is the roll: you have to turn the pipe by the roll angle and then hold that rotation for both bends, which on a hand bender means a pencil line down the pipe at the roll angle (set with a protractor or a torpedo level held at the angle) and the bender centred on that line each time. On a mechanical bender the pipe is clamped, so set the roll once and it stays.
Preguntas
- What makes an offset a rolled offset?
- A plain offset moves the run in one direction — up, or across. A rolled offset moves it in two at once: it rises and shifts sideways between the same pair of fittings, so the jog is tilted out of the vertical plane. You still bend an ordinary offset; you just roll the pipe over first.
- What is the true offset?
- The true offset is the straight-line distance the run actually travels, the hypotenuse of the rise and the roll: √(rise² + roll²). That is the number you feed into the offset math, because the pipe does not know it is tilted — it only knows how far it has to jog.
- What is the roll angle for?
- The roll angle is how far to rotate the conduit — or your bends — off vertical before you bend the offset, so the jog leans the right way. It is atan(roll ÷ rise) measured from straight up. Roll the pipe to that angle in the bender, then bend the offset to the true offset.
- Do I still add shrink on a rolled offset?
- Yes, and against the true offset, not the rise. The run shrinks by the offset shrink of your bend angle applied to the true offset. Add it to your measurement the same as any offset or the far fitting lands short.