Rolling Offset Calculator (pipe travel, true offset & run for 45°, 22½°, 60° fittings)

Understanding the rolling offset calculator — concept and principle

This calculator works out the travel (centre-to-centre length) of the angled piece in a rolling pipe offset, the true offset and the run, from the roll, the set and the fitting angle. Plumbers and pipefitters use it to cut pipe accurately when a line must move sideways and up or down at the same time.

Two offsets become one: with the default inputs the result is Travel 28.28 (run 20 · roll angle 36.9°).

How it is calculated

True offset = √(roll² + set²).
Travel = true offset ÷ sin θ (for 45° fittings, × 1.4142).
Run (advance) = true offset ÷ tan θ.
Fitting constant = 1 ÷ sin θ.
Roll angle = arctan(roll ÷ set), how far to turn the fittings from vertical.

The principle

A rolling offset combines two perpendicular offsets: the roll (sideways) and the set (up or down). Because they are at right angles, the real offset that the fittings make is the diagonal between them, found with Pythagoras. The angled piece of pipe and the true offset then form a right triangle with the fitting angle: the travel is the hypotenuse and the run is the distance the offset advances along the pipe line. For 45° fittings the travel is always 1.4142 times the true offset, and the run equals the true offset.

Worked example

Default inputs: roll 12, set 16, 45° fittings.

True offset = √(12² + 16²) = √400 = 20.
Travel = 20 ÷ sin 45° = 20 × 1.4142 = 28.28; fitting constant 1.4142.
Run = 20 ÷ tan 45° = 20.
Roll angle = arctan(12 ÷ 16) = 36.9°.

Each point is the calculator re-run with only “Set — vertical offset (same unit)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Set — vertical offset (same unit)	Travel (centre to centre)
4	17.89
8	20.4
12	24
16	28.28
20	32.98
24	37.95
32	48.33

How to read the result

Travel is centre to centre. Subtract the take-off (make-up) of both fittings to get the cut length of pipe. Turn the fittings by the roll angle so the offset points the right way. Results are in the same unit you entered, inches or centimetres.

Common mistakes

Adding roll and set instead of using the diagonal.
Cutting the pipe to the travel without subtracting fitting take-offs.
Using the wrong constant for 22.5° or 60° fittings.
Measuring offsets from pipe edges instead of centre lines.

Keep in mind: Pipework must meet local plumbing codes and pressure ratings. Check measurements on site before cutting.

Frequently asked questions

How do I calculate a rolling offset?

Find the true offset with √(roll² + set²), then divide by the sine of the fitting angle.

What is the 45° constant?

1.4142; multiply the true offset by it to get the travel.

Why subtract the fitting take-off?

Travel is centre to centre; part of that length is inside the fittings.

Sources: Right-triangle trigonometry (Pythagorean theorem; sine and tangent of the fitting angle), any trigonometry textbook

Checked 9 Nov 2026. Right-triangle trigonometry (Pythagorean theorem; sine and tangent of the fitting angle) applied to the two perpendicular offsets of a rolling offset.

Your numbers