# What is my rolling offset travel?

Rolling offset calculator: the true offset, the travel (centre-to-centre pipe length) and the run of a rolling pipe offset from its rise and roll, with 45°, 60°, 22.5° or any fittings.

- Page: https://www.acalculator.org/construction/rolling-offset-calculator
- JSON spec: https://www.acalculator.org/construction/rolling-offset-calculator.json
- Version: 3b54aa9891a6

## Default answer

Example with the default inputs (Rise 12 in, Roll 9 in, Fitting angle 45°): The travel is 21.213 in for a true offset of 15 in and a run of 15 in.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| rise | Rise | The offset in one direction, such as up and down, centre to centre. |
| roll | Roll | The offset in the other direction, such as sideways, centre to centre. |
| a | Fitting angle | The angle of the two fittings that make the offset. |
| deg | Angle, degrees | The fitting angle, more than 0° and less than 90°. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| travel | Travel | True offset ÷ sin θ: the centre-to-centre length of the angled pipe. |
| trueOffset | True offset | √(rise² + roll²). |
| run | Run (setback) | True offset ÷ tan θ: how far along the line the offset takes. |
| multiplier | Travel multiplier | 1 ÷ sin θ: travel = true offset × this. |
| rollAngle | Roll angle | The angle to turn the offset off vertical: arctan(roll ÷ rise), in degrees. |

## Method

True offset = √(rise² + roll²); travel = true offset ÷ sin θ; run = true offset ÷ tan θ.

## Assumptions

- Both fittings have the same angle θ, and rise and roll are measured centre to centre of the pipe.
- Travel is centre to centre; take off each fitting’s make-up (take-out) to get the length of pipe to cut.

## Worked examples

1. rise = 0.3048, roll = 0.2286, a = 45 gives trueOffset = 0.381, travel = 0.538815, run = 0.381. Source: OpenStax, Algebra and Trigonometry 2e, section 7.2 Right Triangle Trigonometry (sin θ = opposite ÷ hypotenuse, tan θ = opposite ÷ adjacent) and the Pythagorean theorem, https://openstax.org/books/algebra-and-trigonometry-2e/pages/7-2-right-triangle-trigonometry (retrieved 2026-10-03).
2. rise = 0.2032, roll = 0.1524, a = 60 gives trueOffset = 0.254, travel = 0.293294, run = 0.146647. Source: OpenStax, Algebra and Trigonometry 2e, section 7.2 Right Triangle Trigonometry (sin θ = opposite ÷ hypotenuse, tan θ = opposite ÷ adjacent) and the Pythagorean theorem, https://openstax.org/books/algebra-and-trigonometry-2e/pages/7-2-right-triangle-trigonometry (retrieved 2026-10-03).
3. rise = 0.3, roll = 0.4, a = custom, deg = 30 gives trueOffset = 0.5, travel = 1, multiplier = 2. Source: OpenStax, Algebra and Trigonometry 2e, section 7.2 Right Triangle Trigonometry (sin θ = opposite ÷ hypotenuse, tan θ = opposite ÷ adjacent) and the Pythagorean theorem, https://openstax.org/books/algebra-and-trigonometry-2e/pages/7-2-right-triangle-trigonometry (retrieved 2026-10-03).

## FAQ

### How do you calculate a rolling offset?

Find the true offset with the Pythagorean theorem, √(rise² + roll²). Then the travel is the true offset ÷ sin of the fitting angle, and the run is the true offset ÷ tan of the angle.

### What is the true offset?

The straight-line offset across the diagonal of the box made by the rise and the roll. A 12 in rise and a 9 in roll give a true offset of √(144 + 81) = 15 in.

### What is the 45° offset multiplier?

1.4142 (1 ÷ sin 45°). Multiply the true offset by it to get the travel. For 60° fittings it is 1.1547, for 30° it is 2, for 22.5° it is 2.6131, and for 11.25° it is 5.1258.

### What is the run or setback?

How far along the pipe line the offset takes up: true offset ÷ tan θ. With 45° fittings the run equals the true offset.

### Is the travel the length of pipe to cut?

No, the travel is centre to centre of the fittings. Take off each fitting’s make-up (take-out) to get the pipe length.

### What is the roll angle?

The angle to turn the offset off the vertical so it points at the other line: arctan(roll ÷ rise). For a 12 in rise and 9 in roll it is 36.87°.

## Sources

- OpenStax, Algebra and Trigonometry 2e, section 7.2 Right Triangle Trigonometry: sin = opposite ÷ hypotenuse, tan = opposite ÷ adjacent, retrieved 2026-10-03. https://openstax.org/books/algebra-and-trigonometry-2e/pages/7-2-right-triangle-trigonometry
- NIST Special Publication 811 (2008), Appendix B: 1 in = 25.4 mm exactly, retrieved 2026-10-03. https://www.nist.gov/pml/special-publication-811