Station Chainage & Offset Calculator
Converts a chainage and offset along a straight grid line into easting and northing, and back again for checking.
Inputs
Set out a point from chainage and offset, or check a point back to chainage and offset — along a straight grid line or a polyline.
Enter the values and press Calculate.
Or load an example to see a worked result.
Batch from CSV
One row per calculation, with a header row. Values use the units currently selected in the form above. Up to 10,000 rows; nothing is uploaded.
How the method works
A fixed worked example to explain the method — it is not your result.
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Choose a mode: set-out (chainage and offset → coordinates) or check (coordinates → chainage and offset), along a straight line or a polyline.
- Enter the line's start easting and northing and its grid bearing, clockwise from north.
- Optionally enter the chainage at the start of the line, so the station is shown as well as the distance.
- Enter the distance along the line and the offset (+ right, − left), or the check point's coordinates, then press Calculate.
- For a polyline, paste its vertices in order as "E, N" or "ID, E, N" lines. Near a bend the tool lists every equally close projection rather than picking one; optionally declare the segment to project onto.
- Keep a result as A to compare with a second case, or run a whole CSV of points through the same calculation with Batch.
How it works
With bearing A: E = E₀ + s sin A + o cos A and N = N₀ + s cos A − o sin A, where s is the distance along the line and o the offset, positive to the right looking along it.
Check mode reverses it: s = ΔE sin A + ΔN cos A and o = ΔE cos A − ΔN sin A.
Station = start chainage + s. Negative distances (behind the start) and negative offsets (left) are allowed.
Polyline: chainage accumulates along the segments. A check point projects onto the closest segment (interior segments end at their vertices; the first and last extend beyond the ends). Inside a bend two segments can be equally close at different chainages, and outside a bend both meet at the vertex — every tie is reported, and zero-length segments are refused.
A straight line or polyline on the grid — not a curved road or rail alignment — and the distances are grid distances in the coordinates' own CRS.
Worked example
Start (1000, 2000), bearing 0°, 100 m along, 5 m right, start chainage 1000. The peg is at E 1005.000, N 2100.000, station 1100.000. Check mode on (1005, 2100) returns 100 m along and +5 m (right). On the polyline (0, 0) → (0, 100) → (100, 100), the point (5, 95) is 5 m right of BOTH segments — at chainage 95 on the first and 105 on the second — so both are listed.
Common mistakes
- Reading a positive offset as left. It is right of the direction of increasing chainage.
- Confusing the station (start chainage plus distance) with the distance itself.
- Using this for a curve. A curved alignment needs its own geometry (a densified polyline is only an approximation of it).
Frequently asked questions
Which way is a positive offset?
To the right when facing along the increasing-chainage direction of the line.
Related tools
- Bearing & Distance to Coordinates Calculator
- Coordinate Offset Calculator
- Area by Coordinates Worksheet
- Bowditch Adjustment Calculator
- Coordinates to Bearing & Distance Calculator
- Easting/Northing Distance Calculator
Explore more in Surveying, Coordinates, GIS & CAD.
Cite this tool
Zerdly. (2026). Station Chainage & Offset Calculator. Retrieved from https://www.zerdly.com/tools/station-chainage-offset-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.