Rolling Offset Calculator
Find the true offset, travel and run of a pipe rolling offset.
Standard 22½°, 45°, 60° and 90° bends, custom angles, and metric or imperial lengths.
Updated October 24, 2026
What a rolling offset is
A rolling offset joins two pipes that are out of line in two directions at once — sideways and up or down. Enter how far the second line sits in each direction and the bend of the fittings you plan to use, and this page returns the true offset across the two lines, the run between the bends, and the travel length of pipe that connects them.
A plain offset moves a line in one direction, so one right triangle describes it. A rolling offset needs two: the horizontal and vertical offsets are the legs of the first, and their diagonal — the true offset — becomes a leg of the second, with the fitting bend fixing the shape of that second triangle. That is why the answer is not simply the two offsets added together, and why changing the fittings changes the pipe length even when the route does not move.
It is a layout tool for pipefitters, plumbers, HVAC and process installers, and anyone routing screwed, welded or grooved pipe between two fixed points. The page keeps all three lengths live together, lets you pick a standard bend or type your own angle, and allows each box to carry its own length unit — so a route measured in inches can still be read in feet or millimetres.
3 live lengths
True offset, run and travel; each can also be entered
5 bend choices
22 ½°, 45°, 60°, 90° or any custom angle
6 length units per box
mm, cm, m, in, ft and yd, independently
A rolling offset is not a double offset
"Double offset" usually means two offsets in line with each other. A rolling offset is one offset that moves in two perpendicular directions at the same time, so the pipe has to turn through a compound diagonal. The true offset on this page is the single straight-line distance between the two centrelines — the diagonal you could measure with a tape stretched between them.
Entering the two offsets and the bend
Measure the roll, or horizontal offset
Measure between the two pipe centrelines in the sideways direction — perpendicular to the direction the pipe is heading. It is one leg of the offset triangle. Do not measure to the outside of a pipe or to the face of a fitting; the geometry here is centreline geometry.
Measure the set, or vertical offset
Measure the rise or fall between the same two centrelines, again perpendicular to the run and to the horizontal offset. Enter it as a positive amount whether the second line is above or below the first; the calculation only needs the distance.
Choose the fitting bend
Pick 22 ½°, 45°, 60° or 90° if those are the elbows you will use. If you are bending your own pipe, or using fittings that are not one of those four, choose the custom option: the bend angle box then appears and accepts any angle from 0° to 90°. The same bend angle is assumed at both ends of the offset.
Read — or enter — the three lengths
The true offset is the diagonal across the two measured offsets. The run is how far the line advances between the two bends, measured along the direction the pipe is heading. The travel is the length of the connecting pipe between the two bend points, before fitting allowances. All three boxes are live: enter the two offsets and read the answers, or type a travel, a run or a diagonal you already know and let the page recover the rest. The fitting bend stays the anchor either way.
A 100 cm by 50 cm offset with 45° fittings
With a 100 cm horizontal offset and a 50 cm vertical offset, the diagonal is the square root of the sum of their squares:
A 45° bend has a tangent of 1, so the run equals that true offset, and the travel is the diagonal of the second triangle:
The same arithmetic in inches: offsets of 12 in and 16 in give a 20 in true offset, and a 45° bend gives a 20 in run and a 28.2843 in travel. The numbers scale with the unit; the shape of the answer does not.
The travel is not yet the cut length
The travel runs between the two bend points, not between the ends of the pipe. Each fitting consumes some pipe: the socket, thread, weld prep or the curve of the elbow. To turn the travel into a cut length, allow for the fittings you are actually using and add whatever trim the joint needs. Fitting take-out varies with the fitting size, type and manufacturer, so take it from the fittings in your hand rather than from this page.
The three lengths and their formulas
The page solves two right triangles that share the true offset. It works in whichever direction you need: the two measured offsets give the diagonal and the bend angle fixes the run and travel, or a known run or travel gives the diagonal back and the offsets follow from it.
The first triangle: true offset
The horizontal and vertical offsets are the legs, and the true offset is the hypotenuse. If you measured the diagonal instead, the same triangle solves a missing leg:
A leg cannot be longer than the diagonal. If one is, the square root has no real result and the page leaves that box blank with a note instead of inventing a side — a useful check that the three measurements belong together.
The second triangle: run and travel
The bend angle sets the ratio between the true offset and the run. At 45° the tangent is 1, so the run equals the true offset; at 60° it is shorter than the true offset; at 22 ½° it is much longer. A 90° fitting turns immediately, which leaves a run of exactly zero.
The travel is the diagonal of that same second triangle. Written against the sides it is, which is the same length; the page uses the sine form because it also runs backwards.
Both results therefore work as inputs. A known run recovers the true offset with, and a known travel recovers it with. The other length then follows from the true offset and the bend.
Multipliers for the standard bends
Multiply the true offset by these constants to get the travel, and by the run constants to get the run. They are rounded to six decimal places; the page works from the angle itself, so its answer can differ in the last displayed digit.
| Fitting bend | Travel multiplier | Run multiplier |
|---|---|---|
| 22 ½° | 2.613126 | 2.414214 |
| 45° | 1.414214 | 1.000000 |
| 60° | 1.154701 | 0.577350 |
| 90° | 1.000000 | 0.000000 |
For a 150 cm true offset, the 22 ½° row gives roughly 391.97 cm of travel and 362.13 cm of run, while the 60° row gives 173.21 cm and 86.60 cm. That is the fitting choice doing most of the work: the offsets did not change, only the angle through which the pipe turns.
Symbols used on this page
The bend angle is an input, not an answer
The page never works the fitting angle back out of the lengths. The angle belongs to the elbows you own or the bend you can make, so it is selected first; the lengths follow. If you need to know what angle a chosen route implies, draw the two triangles and compare the true offset with the run you can afford — the custom option then lets you enter that angle and check the travel it produces.
Worked examples
Choosing the bend for a fixed route
Situation: A line has to step 120 cm sideways and 90 cm vertically. The offsets are fixed by the existing pipe; only the elbows are a choice.
Entered
The page returns
The two offsets give a 150 cm true offset. The table compares what each standard bend does with that same diagonal.
| Bend | Run (cm) | Travel (cm) | What it needs |
|---|---|---|---|
| 22 ½° | 362.132 | 391.969 | A long free run and the longest pipe |
| 45° | 150 | 212.132 | The usual choice: run equals true offset |
| 60° | 86.6025 | 173.205 | A tighter route with a sharper turn |
| 90° | 0 | 150 | An immediate right-angle turn |
In practice: Where the run is tight, a sharper bend shortens both the run and the travel. Where the line must turn gently — for flow, cleaning or the fittings you have — the 22 ½° option needs a long free run and much more pipe.
Working back from a measured diagonal
Situation: The route is awkward to square off, but the diagonal between the two centrelines measures 150 cm and the vertical offset is 90 cm. The horizontal offset is the missing leg.
Entered
The page returns
With a 45° bend the page then shows a 150 cm run and a 212.132 cm travel. If both measured offsets and the diagonal are entered at once and they do not agree, the newest entry stays and one of the earlier boxes is recalculated so the triangle closes.
In practice: Type the diagonal into the true offset box together with the offset you can measure, and the other offset is solved. This is useful when a tape reaches corner to corner more easily than it reaches each perpendicular direction.
A custom 30° bend
Situation: The elbows on the truck are 30° rather than any standard bend, and the route still has a 150 cm true offset.
Entered
The page returns
In practice: A 30° bend needs a longer run than a 45° bend for the same offset, and it also needs a longer travel: at 30° the travel is exactly twice the true offset. Check the run has room before committing to the gentler angle.
Measurements that change the answer
Measure centreline to centreline
The two offsets are distances between pipe centrelines, not between outer walls or fitting faces. Measuring to an outside edge adds half a pipe diameter to one offset and quietly changes the travel, even though the tape reading looks reasonable.
Use the same bend at both ends
The calculation assumes the same bend angle at each bend, which is what lets one angle describe both triangles. Mixing a 45° and a 60° elbow changes the geometry, and this page does not model that combination.
Allow for fitting take-out
The travel is the distance between bend points. The piece you cut also has to reach into the fittings, so add the take-out or socket allowance for the elbows you are actually using, and mark the bend orientation before cutting.
Check the run has somewhere to go
The run is measured along the direction the pipe is heading, before the second bend brings it back on course. A 22 ½° offset can need more than twice the true offset of free run; on a crowded rack that space is often the real constraint, not the pipe length.
Once the travel is known, the pipe weight follows
If the connecting pipe has to be ordered, handled or supported, the same length can be turned into a weight. The pipe weight calculator takes the pipe outside diameter, wall thickness and length and returns the weight of the run and its weight per foot or per metre.
The quickest sanity check
Do the two offsets and the true offset form a triangle you believe? Then check the travel against the bend: a 45° offset always has a travel of about 1.414 times the true offset, a 60° offset about 1.155 times, and a 90° offset exactly once. If the page shows something far outside those ratios, the bend angle or a unit is the first thing to look at.
Questions
What happens if I type a travel or run that disagrees with the offsets?
A triangle can only hold so many independent measurements. When a new value over-specifies it — both offsets, the bend, and then a travel — the page keeps the value you just typed and recalculates one of the earlier entries, which turns from an input into a result. That is the honest outcome: the two sets of numbers cannot both be right. Check which box changed before you cut; if the recalculated box was one you trust, re-measure instead of forcing both values.
Does the pipe diameter or wall thickness change the answer?
Not for the three lengths. The calculation is centreline geometry: a 50 mm pipe and a 300 mm pipe with the same offsets and the same bend angle have the same true offset, run and travel. Diameter and wall thickness matter when you convert the travel into a cut length, check clearance or choose supports — not in the geometry itself.
What if one of the offsets is zero?
Then you have a plain single-direction offset rather than a rolling one. The true offset equals the nonzero offset, and the run and travel still follow from the bend angle as usual. The page does not require both offsets to be positive; it simply reports the two-direction geometry for whatever you enter.
What happens with a 0° bend?
A 0° fitting is a straight coupling: it cannot create an offset at all. The tangent of 0° is zero, so the run would require dividing by zero and has no defined length. The page accepts 0° as an input but leaves the run blank with an explanation, and the travel waits with it. If you are checking a very slight bend, enter the real small angle instead of zero.
Where the numbers stop
- This is a layout calculation, not a cut list. It gives the travel between two theoretical bend points and does not subtract fitting take-out, socket depth, thread engagement, weld gaps or any trimming allowance. Add those from the fittings and the joint detail you are using.
- It assumes two equal bends and perpendicular offsets. Real elbows have a bend radius, so the sharp-corner triangles are a layout approximation; unequal fittings, compound angles and offsets that do not sit at right angles to the run are outside this model.
- Small measurement errors grow. With a 150 cm true offset, changing the bend from 45° to 60° shortens the travel from 212.132 cm to 173.205 cm — about 18% — and an angle or centreline mistake moves the answer in the same way. Re-measure before cutting rather than adjusting the number afterwards.
- Check it against the job, not just the page. On pressure systems, expansion loops, supports or anything covered by a project specification, have the layout and the cut lengths checked by a qualified pipefitter or engineer before fabrication. The page does not assess pipe stress, support spacing, code compliance or whether the route is buildable in the space available.
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