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Chainage & Offset Calculator

Convert a plane-grid point to chainage and signed perpendicular offset on a two-point or multi-segment alignment, or calculate coordinates from chainage and offset. The alignment is an ordered open polyline of straight segments.

FHWA Bridge Geometry Manual · FHWA-HIF-22-034 · April 2022 · §§5.2–5.5

Uses only this tool title and its public link. Inputs, results, coordinates and filenames are not included. Sharing starts only when you press the button.

Free advisory field tool — every result is computed in your browser from the inputs you provide and is advisory and unverified, not for survey deliverables. Where a published guideline applies, results only ever read “within guideline” or “exceeds guideline — review”. The full working is shown for every calculation so each step can be re-checked. Registered surveyor confirmation required before reliance.

Piecewise-straight alignment

Ordered vertices and starting chainage

Use plane-grid coordinates in one consistent CRS and unit. Segments run in the entered order. Looking along increasing chainage, positive offset is left and negative offset is right.

CSV or whitespace; optional E,N header. Up to 1000 vertices, 2,000 physical rows and 100,000 characters.

Conversion direction

Enter calculates from a single-line field. Enter still adds a new line in pasted lists.

Calculated position

Chainage, signed offset and coordinates

OK

The result uses finite alignment segments only. Review the selected segment and full working before relying on the coordinates.

Chainage (m)
1050
Signed offset (m)
20Left
Alignment easting (m)
500050
Alignment northing (m)
6960000
Selected segment
12 eligible
Show the working
  1. selected segmentfinite segment with the smallest absolute perpendicular offset1
  2. segment delta EE2 - E1100
  3. segment delta NN2 - N10
  4. segment lengthhypot(delta E, delta N)100
  5. distance into segment(P - A) dot unit tangent, bounded to the finite segment50
  6. chainagesegment start chainage + distance into segment1050
  7. signed offset(P - A) dot left normal; positive left, negative right20
  8. projected eastingA_E + unit_E * distance500050
  9. projected northingA_N + unit_N * distance6960000
  10. eligible segmentssegments whose perpendicular foot lies within both endpoints2

Working trace rendered from the same computation as the result above — re-check any step by hand before relying on it.

Convention: chainage increases through the entered vertices. Looking in that direction, positive offset is left and negative offset is right. Projection is limited to each finite segment; the nearest eligible perpendicular projection is used.

Source record: FHWA-HIF-22-034, Bridge Geometry Manual, April 2022, §5.2 printed pp 48–50, §5.3 printed pp 51–52 and §5.5 printed pp 55–57. The publication gives tangent run, offset and projection methods plus worked examples; no separate effective date is stated. Curves are not inferred between the supplied vertices.

Advisory output — confirm independently before reliance.

Method

How to use the chainage and offset calculator

Enter an ordered plane-grid alignment, choose a conversion direction and review the selected segment and result.

  1. Paste the ordered alignment

    Enter at least two easting and northing vertices in increasing alignment order and supply the starting chainage.

  2. Choose a conversion direction

    Select point to chainage and offset, or chainage and offset to point, then enter the values required for that direction.

  3. Review segment selection

    Inspect the selected finite segment, signed side convention, result coordinates and calculation trace before transferring a value.

Australian surveying FAQ

Questions about Chainage & offset

How does a chainage offset calculator in Australia treat an alignment?

This chainage offset calculator treats the entered Australia working data as ordered, finite, piecewise-straight plane-grid segments and reports which segment was selected.

Which side of the alignment is a positive offset?

Looking along increasing chainage, a positive signed offset is left and a negative signed offset is right. Zero lies on the selected segment.

Does the calculator model horizontal curves?

No. It operates on the straight segments formed by consecutive entered vertices and does not infer curve geometry, datum, zone or ground scale.

Related
Offset from design line Radial set-out sheet Vertical curve calculator Docs hub — working-data guides All field tools

Safety & scope

SurveyMarkup helps prepare and review working information. Every professional decision remains with the registered surveyor, and original data and final outputs require qualified review.

Assistance only - professional review remains required.