Rolling Offset Calculator

A rolling offset calculator returns the travel and run for a pipe that shifts in two planes at once. It combines the vertical offset and horizontal roll into one true offset with the Pythagorean theorem. A 12 in. vertical offset with a 12 in. roll at 45° needs about 24.0 in. of travel and 16.97 in. of run.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Travel (Pipe Length Between Fittings)

24.000 in

Breakdown
Travel (Pipe Length Between Fittings)	24.000 in
True Offset	16.971 in
Run	16.971 in

How to Calculate Rolling Offset

A rolling offset happens when a pipe needs to change direction in two planes at once, both vertically (up and down) and horizontally (side to side). The Pipe Offset calculator handles the simpler single-plane offset. The trick pipefitters use is to combine the vertical offset and horizontal roll into a single "true offset" with the Pythagorean theorem, `√(vertical² + horizontal²)`. The legs are perpendicular, so the theorem applies. Once the true offset is found, the same standard offset trigonometry applies: `travel = true offset ÷ sin(angle)` and `run = true offset ÷ tan(angle)`.

Example: 12 in. vertical offset combined with a 12 in. horizontal roll

A 12 in. vertical offset combined with a 12 in. horizontal roll, using 45° fittings: 1. True offset: √(12² + 12²) = √288 ≈ 16.97 in 2. Travel: 16.97 ÷ sin(45°) = 16.97 ÷ 0.7071 ≈ 24.0 in 3. Run: 16.97 ÷ tan(45°) = 16.97 ÷ 1 ≈ 16.97 in That rolling offset needs about 24.0 in. of travel (pipe length) and 16.97 in. of run.

What Is Rolling Offset?

A rolling offset calculator finds the travel (diagonal pipe length between fittings) and run (horizontal distance) for a pipe that needs to shift in two directions at once. Those directions are up or down and side to side. It uses standard fitting angles: 22.5°, 30°, 45°, or 60°. It's the compound version of the simple offset.

Rolling Offset: Pros and Cons

Pros

Uses the same true-offset technique working pipefitters use, rather than treating the two planes as separate, unrelated offsets
Covers all four standard fitting angles used in the trade
Works for any combination of vertical and horizontal offset distances

Cons

Doesn't account for fitting takeout, the small amount of extra length a fitting itself adds beyond the pure geometric travel. Actual cut pipe length is typically shorter than the calculated travel by each fitting's takeout dimension
Assumes both offset legs are measured perpendicular to each other and to the main pipe run. An offset at an unusual angle needs different math
For a simple single-plane offset, not a compound one, see the Pipe Offset calculator instead. It's a more direct calculation without the true-offset step

Rolling Offset: What a Pro Checks

Subtract each fitting's takeout, its center-to-end length from the spec sheet, from the calculated travel before cutting. Fittings add a small amount of length beyond the pure geometric travel calculated here.
Confirm both offset legs are truly perpendicular to each other and to the main run before using this. An offset measured at an unusual angle needs different math than the standard true-offset formula.

Frequently Asked Questions

What is a rolling offset in plumbing?

A pipe offset that changes direction in two planes at once, both vertically and horizontally, rather than a simple single-plane offset. It's common when a pipe needs to route around an obstruction that isn't directly above or below the original line.

How do you calculate a rolling offset?

Combine the vertical offset and horizontal roll into a "true offset" using the Pythagorean theorem, √(vertical² + horizontal²). Then apply the standard offset formulas: travel = true offset ÷ sin(angle), and run = true offset ÷ tan(angle).

What's the difference between a rolling offset and a regular offset?

A regular, single-plane offset only shifts a pipe in one direction, either up and down or side to side. A rolling offset combines both into one compound move. It requires the true-offset calculation to combine the two perpendicular legs first.

Does fitting angle affect how much travel I need?

Yes. A shallower angle, like 22.5°, needs more travel and run to achieve the same true offset than a steeper angle, like 60°. Travel = true offset ÷ sin(angle), and sin decreases as the angle gets smaller.

Do I need to subtract fitting takeout from the travel measurement?

Yes, for an exact cut length. Fittings themselves add a small amount of length beyond the pure geometric travel calculated here. Subtract each fitting's specific takeout dimension, found on the fitting's spec sheet, from the travel figure to get the actual pipe length to cut.

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