What are travel, offset and run?

In a simple offset, the offset (or set) is how far the pipe shifts sideways, the travel is the diagonal pipe length between the two fittings, and the run is how far the pipe advances along its original direction. Together they form a right triangle with the fitting angle.

How is travel calculated from the offset?

Travel equals offset divided by the sine of the fitting angle, which is the same as offset times the cosecant of the angle. For 45 degrees the cosecant is 1.414, so a 10 inch offset needs a 14.14 inch travel between fitting centers.

Why do plumbers memorize constants like 1.414?

Multiplying the offset by a fixed constant for each angle is faster than reaching for a calculator on the job. 1.414 for 45 degrees, 2.613 for 22.5 degrees and 1.155 for 60 degrees are the classic travel constants pipefitters keep on hand.

Do I cut the pipe to the travel length?

Not exactly. Travel is the center-to-center distance between fittings. You must subtract the fitting take-out (the lay length each fitting consumes) from both ends to get the actual pipe cut length, which is why this tool lets you enter a fitting allowance.

What is a rolling offset?

A rolling offset shifts the pipe both horizontally and vertically at once. You first combine the horizontal and vertical offsets into a single true offset with the Pythagorean theorem, then apply the same travel constant. This tool covers the simple in-plane offset; compute the true offset first for rolling work.

What is the Pipe Offset / Travel Calculator (Plumbing Isometric)?

Solves the pipe offset triangle for bends at 11.25°, 22.5°, 30°, 45° and 60° using the cosecant, cotangent and tangent constants to return travel (diagonal cut length), run and set, the way plumbers lay out drains and supply offsets. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Pipe Offset / Travel Calculator (Plumbing Isometric)

Name: Pipe Offset / Travel Calculator (Plumbing Isometric)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

When a pipe has to jog around an obstruction, the plumber sets two fittings and runs a diagonal between them. This calculator solves that offset triangle for any standard fitting angle, giving the travel (diagonal cut length), the run, and the net pipe length after subtracting fitting take-out.

How it works

The offset, travel and run form a right triangle where the fitting angle is measured from the original pipe line:

travel = offset / sin(angle)   = offset × cosecant(angle)
run    = offset / tan(angle)   = offset × cotangent(angle)
cut    = travel − 2 × fitting take-out

The classic memorized constants fall straight out of this:

Fitting angle	Travel constant (CSC)	Run constant (COT)
11.25°	5.126	5.027
22.5°	2.613	2.414
30°	2.000	1.732
45°	1.414	1.000
60°	1.155	0.577

Multiply your offset by the travel constant to get travel without needing trigonometry on the job. Multiply by the run constant to get the advance along the original pipe direction.

Worked examples

Example 1 — 45° offset, 10-inch set. Travel = 10 × 1.414 = 14.14 inches, center to center. Run = 10 × 1.000 = 10 inches advance along the original line. With 1-inch take-outs on each fitting, the pipe cut length is 14.14 − 2 = 12.14 inches.

Example 2 — 22.5° offset, 6-inch set. Travel = 6 × 2.613 = 15.68 inches. Run = 6 × 2.414 = 14.48 inches. The gentler angle advances the pipe significantly before completing the offset, which is why 22.5° offsets are preferred on drain lines where long diagonal runs improve flow.

Example 3 — 60° offset, 8-inch set. Travel = 8 × 1.155 = 9.24 inches — compact, but the tight angle can trap debris on drain lines. Better suited to supply lines where tight spaces require a sharp jog.

Rolling offsets

A rolling offset shifts the pipe both horizontally and vertically at once — for example, moving 6 inches left and 8 inches up simultaneously. Solve it by computing the true offset first:

true offset = √(horizontal shift² + vertical shift²)

For 6 and 8 inches: true offset = √(36 + 64) = √100 = 10 inches. Apply the same travel constant to this true offset to get the diagonal pipe length.

Choosing the right fitting angle

22.5° — preferred on drain, waste, and vent lines; long gentle diagonal sustains flow and limits turbulence. Requires more space along the run.
45° — the most common general-purpose offset; good balance of diagonal length and run space.
60° — tight abrupt offset for confined spaces; more turbulence, avoid on waste lines if possible.
11.25° — very shallow offset, rarely used, produces a very long run for a small lateral shift.