acalculator

What is my rolling offset travel?

Type the rise and the roll of the offset, centre to centre, and pick the fitting angle. The rolling offset calculator gives the true offset, the travel (the centre-to-centre length of the angled pipe) and the run.

Your numbers

Units
Travel
21.213 in

The travel is 21.213 in for a true offset of 15 in and a run of 15 in.

True offset
15 in
Run (setback)
15 in
Travel multiplier
1.4142
Roll angle°
36.87

Travel: 21.213 in. The travel is 21.213 in for a true offset of 15 in and a run of 15 in.

How to calculate

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.

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.

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

  • 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.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Rise 12 in, Roll 9 in, Fitting angle 45° gives True offset 15 in, Travel 21.213 in, Run (setback) 15 in.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 8 in, Roll 6 in, Fitting angle 60° gives True offset 10 in, Travel 11.547 in, Run (setback) 5.774 in.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 11.81 in, Roll 15.75 in, Fitting angle Other angle, Angle, degrees 30 gives True offset 19.685 in, Travel 39.37 in, Travel 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)

How it works

The rise and the roll are the two sides of a box; the angled pipe crosses its diagonal. With fitting angle θ:

  • True offset = √(rise² + roll²).
  • Travel (centre to centre) = true offset ÷ sin θ.
  • Run (setback) = true offset ÷ tan θ.
  • Travel multiplier = 1 ÷ sin θ.
  • Roll angle = arctan(roll ÷ rise), in degrees from vertical (90° when the rise is 0).

The fitting angle is 45°, 60°, 30°, 22.5° or 11.25°, or an angle you type (0.01° to 89.99°). Both fittings have the same angle.

Rules

Rise and roll are 0 to 1 km each. If both are 0 there is no answer: "Type a rise or a roll more than 0."

Output format

Lengths show in inches (US) or millimetres (Metric) to 3 decimals; the multiplier to 4 decimals; the roll angle to 2 decimals. The maths uses square roots and trigonometry in floating point, rounded half up for display.

Worked examples by hand

A 12 in rise, 9 in roll, 45° fittings. True offset √(144 + 81) = 15 in. Travel 15 ÷ 0.70711 = 21.213 in. Run 15 ÷ 1 = 15 in. Roll angle arctan(9 ÷ 12) = 36.87°.

An 8 in rise, 6 in roll, 60° fittings. True offset 10 in. Travel 10 ÷ 0.86603 = 11.547 in. Run 10 ÷ 1.73205 = 5.774 in.

A 0.3 m rise, 0.4 m roll, 30° fittings. True offset 0.5 m. Travel 0.5 ÷ 0.5 = 1 m; multiplier 2.

Other questions people ask

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°.