Irish Grid / ITM Converter
Converts between Irish Grid (TM75), ITM and latitude/longitude, reads lettered grid references and converts local CSV files.
ITM and Irish Grid are different systems, not two names for one. Irish Transverse Mercator (EPSG:2157) uses the GRS80 ellipsoid and a false origin of 600000 E / 750000 N. The legacy Irish Grid (TM75, EPSG:29903) uses the Airy Modified 1849 ellipsoid and 200000 E / 250000 N, and reaching it needs a real datum transformation. The same Dublin point is 715826 E / 734697 N in ITM and 315900 E / 234671 N in Irish Grid. Choose the system your data is actually in.
WGS 84 → IRENET95 / Irish Transverse Mercator. WGS84/GPS compatibility conversion. The input reference-frame realisation and epoch are unspecified; this is not a survey-accuracy transformation. The operation used, IRENET95 to WGS 84 (1) (EPSG:1678), has a published accuracy of 1 m.
Paste a coordinate pair
Result
Choose the systems, enter a coordinate and press Convert. Everything is computed in this browser. Use Load Dublin example if you want a worked case to start from.
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 the system your data is in, then the system you want. ITM and Irish Grid are different systems, not two names for one.
- Enter the coordinate: decimal degrees, degrees and minutes, degrees/minutes/seconds, easting and northing in metres, or a lettered Irish grid reference.
- Press Convert. Editing any field marks the result out of date rather than quietly replacing it.
- For a batch, open batch conversion and paste rows or choose a local CSV. Nothing is uploaded.
How it works
Irish Transverse Mercator (ITM, EPSG:2157) uses the GRS80 ellipsoid with a false origin of 600000 m E / 750000 m N and a scale factor of 0.99982.
The legacy Irish Grid (TM75, EPSG:29903) uses the Airy Modified 1849 ellipsoid with a false origin of 200000 m E / 250000 m N and a scale factor of 1.000035. Converting between the two is a real datum transformation, not an offset.
Cross-datum routes use the published operation TM75 to WGS 84 (2) / TM75 to ETRS89 (2) (EPSG:1954 / EPSG:1953), a seven-parameter Position Vector Helmert with a published accuracy of 1 m. A more accurate grid-based operation exists and is named in the method notes; it is not used because it needs a grid file this browser-only tool does not ship.
A route between WGS84 and an Irish frame is an approximation: the arithmetic is a zero shift (EPSG:1678) but the input's reference-frame realisation and epoch are unspecified, so the published accuracy is 1 m.
Definitions and operations are resolved by EPSG authority code from EPSG dataset v12.029 and validated against PROJ 9.8.1 fixtures committed with the code.
Horizontal coordinates only. No height conversion of any kind is performed.
Worked example
Dublin (53.3498, −6.2603) in both grids. In ITM that is 715,826.507 m E, 734,697.593 m N. In Irish Grid (TM75) the same point is 315,900.562 m E, 234,671.359 m N — which is why choosing the right system matters.
Frequently asked questions
Can I convert the old Irish Grid (TM75)?
Yes. Irish Grid (TM75, EPSG:29903) is a fully supported source and target, in both directions and directly to and from ITM. It uses the published EPSG:1953 / EPSG:1954 seven-parameter transformation, whose accuracy is 1 m.
Why do ITM and Irish Grid give such different numbers?
They have different false origins, different scale factors and different ellipsoids. Dublin is 715,826 m E in ITM and 315,900 m E in Irish Grid. The difference is not a constant you can add — it varies across the country, because the two systems differ by a rotation and a scale change as well as a shift.
Is a WGS84 or GPS coordinate exact here?
No. WGS84/GPS compatibility conversion treats your input as if it were in the Irish reference frame. The input's frame realisation and epoch are unspecified, so this is not a survey-accuracy transformation. The published accuracy of the operation is 1 m.
What does a lettered reference like O 123 456 mean?
It names a cell in the Irish Grid, not a point. The letter is one of 25 hundred-kilometre squares (A to Z with I omitted) and the digits split equally between easting and northing. O 123 456 is a 100 m cell whose south-west corner is 312,300 m E, 245,600 m N; its centre is 312,350 m E, 245,650 m N. Because it describes a cell, it is less precise than a full metre coordinate. Lettered references belong to Irish Grid only — ITM has no lettered form.
Are my files uploaded?
No. Both single points and CSV batches are processed in this browser using the File API. No account, no conversion server, and no coordinates, filenames or rows leave your device.
Does this convert height?
No. This is horizontal coordinate conversion only. No ellipsoidal or orthometric height is computed, and no Malin Head or Belfast height datum conversion is performed.
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Cite this tool
Zerdly. (2026). Irish Grid / ITM Converter. Retrieved from https://www.zerdly.com/tools/irish-grid-converter-ig-itm/
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.