Rolling Offset Calculator

How to use the rolling offset calculator

What this calculator does

This calculator estimates the geometry required when two parallel pipe centerlines are displaced in both the horizontal and vertical directions. It combines those two perpendicular displacements into the True offset (c), then uses the selected Fitting bend to calculate Travel (T) and Run (R). It is a layout and planning tool, not a complete pipe-cutting specification: it does not automatically include fitting takeout, socket depth, weld gap, pipe-wall effects, code allowances, or field tolerances.

When to use it

Use the calculator when routing pipe around an obstruction, aligning two offset centerlines, checking a spool-layout sketch, or comparing the space required by different elbow angles. The same geometry can support conduit, tubing, and other straight runs joined by equal-angle direction changes, provided you work consistently from centerlines.

How to calculate

1. The calculator opens with a complete demonstration: a 100 cm horizontal offset, a 50 cm vertical offset, and 45° fittings. The example results and Excel workbook are ready immediately.
2. Replace Horizontal offset (h) and Vertical offset (v) with your measured centerline displacements. Enter ordinary decimal numbers using a period as the decimal separator.
3. Choose the common Length unit. Switching units converts the current offset entries and updates every result.
4. Select a standard Fitting bend. Choose Custom angle only when your bend is not listed, then enter the angle in Custom bend angle.
5. Read Travel (T) as the diagonal centerline distance between the two bend points. Review True offset (c), Run (R), the Offset multiplier, and the calculation-detail table for a transparent check.
6. Select Download Excel to save the current typed inputs and calculated values in a validated .xlsx workbook. Reset clears the demonstration data and results; Excel export remains unavailable until a complete valid state is entered again.

Input guide

Horizontal offset (h) is a required nonnegative decimal length, such as 100 cm. A larger value increases the true offset, travel, and run. Measure perpendicular to the vertical offset; do not enter a diagonal measurement here. Vertical offset (v) is the second required nonnegative decimal length, such as 50 cm, and affects the results in the same way. At least one of these two offsets must be greater than zero.

Length unit applies to both inputs and all length outputs. Available units are millimeters, centimeters, meters, inches, and feet. Changing the unit converts the current entries rather than merely relabeling them. Avoid mixing measurements from different unit systems. Fitting bend is the direction-change angle of each fitting, with common options from 22.5° through 90°. Smaller bend angles require more travel and more run. Custom bend angle is required only in custom mode; enter a decimal angle greater than 0° and no more than 90°, for example 37.5°.

Output guide and worked example

True offset (c) is the combined perpendicular displacement, calculated as √(h² + v²). Travel (T) is the required centerline distance along the offset section and equals c ÷ sin(angle). Run (R) is the axial distance consumed by the offset and equals c ÷ tan(angle). The Offset multiplier is 1 ÷ sin(angle), so travel also equals true offset multiplied by this number. These are geometric identities, while any final cut length remains a fabrication estimate after fitting allowances are applied.

The summary pills repeat the current true offset, bend angle, and travel for quick scanning. The calculation-detail table lists each quantity, symbol, value, and formula. Zero is valid for either individual offset, but not for both together. At 90°, run becomes zero because the travel is directly across the true offset.

Learn more

The geometry rests on the OpenStax explanation of sine and cosine and the right-triangle relationship described in the Pythagorean theorem reference. Keep units consistent with the NIST guidance on SI length units, and verify fabrication details against the governing project specification and relevant piping code.