Rolling Offset Calculator
Solve a rolling offset — a pipe run that has to shift sideways and up or down at the same time to clear an obstacle. Enter the roll (horizontal) and rise (vertical) offsets and the fitting angle, and get the true offset, the travel (center-to-center pipe length), the run (advance along the line), the roll angle, and the cut length after fitting take-off — with a by-angle table, a unit table, and a downloadable PDF.
| Angle | Travel | Run | ×offset |
|---|---|---|---|
| Enter offsets to compare angles | |||
| Measure | Inches | Decimal ft | Ft-in |
|---|---|---|---|
| Enter offsets to convert | |||
How to use the rolling offset calculator
Enter the roll (sideways) and rise (vertical) offsets and pick the fitting angle, then add the fitting take-off and how many offsets you’re running. You get the true offset, the center-to-center travel, the run, the roll angle, and the pipe cut length — plus a by-angle table and a unit conversion.
Enter roll & rise
The sideways shift and the up/down shift between the two fittings, in inches or feet.
Pick the fitting angle
Tap 45°, 22½° or another elbow angle. The chip shows the travel multiplier for that angle.
Add take-off & quantity
Enter one fitting’s take-off to get the cut length, and how many identical offsets you’re running.
Read the cut sheet & save a PDF
See travel, run, roll angle and the cut length in inches and feet-inches, compare angles, and download it.
How a rolling offset is solved
The trick is to collapse the two shifts into one. Combine the roll and rise into a single true offset — the diagonal — and the rolling offset then solves exactly like a flat offset using that diagonal and the fitting angle.
Worked example — 12″ roll, 9″ rise, 45° fittings
True offset: √(12² + 9²) = √225 = 15 in
Travel: 15 ÷ sin(45°) = 15 × 1.414 = 21.21 in
Run: 15 ÷ tan(45°) = 15 in
Roll angle: atan(12 ÷ 9) = 53.1° off vertical
Cut (½″ take-off ea): 21.21 − 2 × 0.5 = 20.21 in
A 15-inch true offset needs 21.21 inches of travel — cut the pipe to about 20¼ inches after take-off, with the fittings rolled 53° off vertical.
Rolling offset reference charts
The lookups that come up most — travel and run multipliers by fitting angle, true offsets for common roll-and-rise pairs, and how the pieces fit together.
| Fitting angle | Travel ×offset | Run ×offset | Character |
|---|---|---|---|
| 11¼° | 5.126 | 5.027 | Very gentle, long advance |
| 22½° | 2.613 | 2.414 | Gentle, eases flow |
| 30° | 2.000 | 1.732 | Moderate |
| 45° | 1.414 | 1.000 | Standard — balanced |
| 60° | 1.155 | 0.577 | Steep, short advance |
| 72° | 1.051 | 0.325 | Very steep, tight run |
Multiply the true offset by the travel factor for the center-to-center length. At 45° the run equals the offset exactly; at shallower angles the run grows, which is why a gentle angle needs more space along the line.
| Roll × Rise | True offset | Travel at 45° | Travel at 22½° |
|---|---|---|---|
| 6 × 6 in | 8.49 in | 12.00 in | 22.18 in |
| 12 × 9 in | 15.00 in | 21.21 in | 39.20 in |
| 12 × 12 in | 16.97 in | 24.00 in | 44.35 in |
| 18 × 12 in | 21.63 in | 30.59 in | 56.52 in |
| 24 × 18 in | 30.00 in | 42.43 in | 78.40 in |
| 24 × 24 in | 33.94 in | 48.00 in | 88.70 in |
The true offset is the diagonal of roll and rise — a classic 3-4-5 triangle, like 12×9 giving 15, makes a clean check. Travel is that offset times the angle’s multiplier; subtract take-off for the cut.
| Term | What it is |
|---|---|
| Roll | The horizontal, sideways shift between the two fittings |
| Rise (set) | The vertical, up-or-down shift between the two fittings |
| True offset | The straight diagonal distance combining roll and rise |
| Travel | Center-to-center pipe length along the slope (the hypotenuse) |
| Run | How far the offset advances along the original pipe line |
| Roll angle | How far the offset is rotated off vertical |
| Take-off | A fitting’s lay-in — face to socket center — subtracted from travel |
| Cut length | Travel minus take-off at each end — what you cut the pipe to |
Travel is always the longest of travel, offset and run — it’s the hypotenuse. Cutting to the offset instead of the travel is the classic mistake; always size from the travel.
A rolling offset turns a two-plane problem into a right triangle: the roll and rise combine into the true offset, the pipe runs along the travel at the fitting angle, and you deduct the take-off at each end for the cut length.
- Combine roll and rise first — the diagonal is the true offset, and everything else follows from it.
- Cut to the travel, not the offset — travel is the hypotenuse and always longer; this is the usual mistake.
- Take off both fittings — subtract one take-off at each end, or the pipe runs long and won’t seat.
Everything the calculator works out
One set of offsets gives you the true offset, the travel, the run, the roll angle and the cut length, in both inches and feet-inches — plus a comparison across fitting angles and a report for the job.
The figures behind every offset
Built for anyone routing pipe around an obstacle
A waste line past a beam, a conduit run around ductwork, a process pipe clearing a pump — whenever a run has to shift two ways at once, the roll-rise-angle math is the same, and getting the travel and cut right the first time saves a wasted length of pipe.
Routing a drain or supply line around a joist, beam or another pipe, and needing the cut length right before taking the saw to an expensive length of pipe.
- Default to 45° fittings
- Subtract take-off both ends
- Set the roll angle off vertical
Bending conduit to offset around ductwork or structure in two planes, using the same travel math with a bend deduction instead of a socket take-off.
- Same offset / travel / run math
- Use bend gain, not socket take-off
- Mark the roll before bending
Learning the offset multipliers, or totaling pipe for several identical offsets on a takeoff without re-deriving the trig each time.
- Compare angles side by side
- Read lengths in feet-inches
- Save the PDF cut sheet
7 tips for cutting a rolling offset right
The mistakes that waste a length of pipe — and the checks that get the cut right the first time.
Rolling offset FAQ
The geometry, cutting and fitting questions people ask most when sizing a rolling offset.
A rolling offset is a pipe run that changes direction in two planes at once — it shifts sideways and up or down between the same two fittings — to route around an obstacle a simple offset can’t clear. The pipe between the fittings runs at a compound angle rather than straight.
The sideways shift is the roll and the vertical shift is the rise (or set). Combine them into a single true offset and the rolling offset then solves like an ordinary offset using that diagonal, which is what makes the math workable on the job.
First find the true offset, the diagonal of roll and rise: √(roll² + rise²). Then travel (center-to-center) is true offset ÷ sin(angle), and run — the advance along the line — is true offset ÷ tan(angle).
For a 12-inch roll and 9-inch rise with 45° fittings, the true offset is 15 inches, the travel about 21.2 inches, and the run 15 inches. Subtract each fitting’s take-off from the travel to get the length to cut the pipe.
The true offset is the straight diagonal between the two pipe centerlines — the combined sideways and vertical shift. Travel is the center-to-center pipe length that bridges it along the slope. Run is how far the offset advances along the original pipe line.
Picture a right triangle: offset and run are the two legs, travel is the hypotenuse. Travel is always the longest of the three, which is why you cut pipe to the travel minus take-off, not to the offset.
At 45° the travel is 1.414 times the true offset, so multiply the offset by 1.414 for the center-to-center length. The run at 45° equals the offset exactly, because the two legs of a 45° right triangle are equal.
Each angle has its own constant: 1.414 at 45°, 2.613 at 22½°, 2.0 at 30°, 1.155 at 60°. These are the fast way to size an offset once you know the true offset, and 45° is most common because its factor is easy and the fittings are widely stocked.
Take-off is the lay-in of a fitting — the distance from its face to the center of its socket or hub. The travel is center-to-center of the two fittings, but the pipe only spans socket to socket, so each fitting eats part of that length.
To get the real cut length, subtract one take-off at each end: cut = travel − 2 × take-off. Skip it and the pipe comes out too long and the joint won’t seat. Take-off varies by pipe size, material and fitting type, so measure your actual fittings.
45° is the default — the fittings are everywhere, the 1.414 multiplier is easy, and travel and run are balanced. Use a shallower angle like 22½° when space along the run is tight and you want a gentler, longer diagonal, which also eases flow in drainage pipe.
Steeper angles like 60° give a shorter run but a sharper turn and a travel closer to the offset. The choice is driven by the space to advance along the line and the fittings you can get — pick the angle to fit the obstacle, then size to that angle.
The roll angle is how far the offset is rotated out of vertical — the angle between straight-up and the true-offset diagonal, set by the ratio of roll to rise. It tells you how far around the pipe to rotate the fitting so the offset heads in the right compound direction.
Mark it on the pipe or set it with a protractor or level when you orient the first fitting, so the run shifts both sideways and vertically by the amounts you entered. Get the travel right but the roll wrong and the pipe is the right length but points the wrong way.
Because the travel is the hypotenuse of a right triangle whose other two sides are the true offset and the run. The pipe slopes across the offset rather than jumping straight to it, so the sloped length is always longer — at 45°, about 1.414 times longer.
This is the most common rolling-offset mistake: cutting to the offset instead of the travel leaves the pipe far too short. Always size from the travel, then take off the fittings — and the shallower the angle, the bigger the gap between offset and travel.
Reference Only — Verify Against Your Fittings: This calculator solves the geometry of a rolling offset using true offset = √(roll² + rise²), travel = true offset ÷ sin(angle), and run = true offset ÷ tan(angle). Travel is center-to-center of the fittings; the cut length subtracts the fitting take-off you enter at each end. Take-off and bend deductions vary by pipe size, material, fitting type and how the turn is made (threaded, soldered, solvent-weld, grooved, welded, or conduit bend), so confirm them against your actual fittings before cutting. The calculator does not address pipe sizing, slope or fall requirements for drainage, support spacing, or code compliance. For reference and estimating only; dry-fit and verify every cut against the real fittings and layout before committing a joint.