Irish Grid Reference Finder

Tap once and you get your position in both Irish systems at the same time: the classic Irish Grid reference — J 337 740 style, the format on OSNI and OSi paper maps — and modern ITM coordinates, the format digital mapping uses. Paste any Irish Grid reference or ITM pair and it converts back to a point on the map. It works across the whole island, Northern Ireland and the Republic alike, computes on your device to within a few meters, and keeps working offline once loaded.

Irish Grid vs ITM — which is your map using?

Convert anything

One letter, not two

Unlike Britain's two-letter squares, the Irish Grid covers the island with a single 500 km zone split into 25 lettered 100 km squares (A–Z, skipping I). J holds Belfast and most of the north-east, O holds Dublin, W holds Cork, M holds Galway. The figures work exactly like their British cousins: first half east, second half north, and every extra pair of figures shrinks the square tenfold — J 33 74 is a kilometre square, J 337 740 is 100 m, five-and-five figures is 1 m. Six figures is the everyday standard on both sides of the border.

Irish Grid or ITM — which one do you need?

Ireland runs two systems side by side. The Irish Grid (1965 datum) is what printed OSNI and OSi maps, guidebooks and hill-walking routes use — if you're reading a reference to another person, this is almost certainly the one. ITM (Irish Transverse Mercator) is the modern replacement on the ETRS89 datum: plain east/north numbers with no letters, used by GIS data, surveying and both mapping agencies' digital services. This tool always shows both, so you never have to know in advance which one the form, the map, or the person on the phone expects. Handy tell: ITM eastings run in the 400,000–770,000 range — six-digit pairs that big are ITM, letter-prefixed references are Irish Grid.

Accuracy, honestly stated

Your phone speaks WGS84; the Irish Grid lives on the 1965 datum, offset from it by roughly fifty meters on the ground. This tool applies the standard published Helmert transformation between them — accurate to a few meters across the island, comfortably inside a 6- or 8-figure square (survey-grade work should use OSi/OSNI's official polynomial transformation instead). ITM is easier still: its ETRS89 datum agrees with GPS to well under a meter, so ITM values here are essentially as good as your GPS fix. Test what your phone can actually do on the GPS accuracy page.

The whole island — and only the island

The Irish Grid covers Northern Ireland and the Republic of Ireland, coast to coast — one system, no seam at the border. It does not extend to Great Britain: a position in England, Scotland or Wales gets an honest “outside the Irish grid” answer here, and the OS National Grid page takes over there. Anywhere else in the world, UTM/MGRS is the international equivalent. Mountain rescue on both sides of the border works from Irish Grid references — the emergency location page covers how to read your position to a rescue team.

Frequently asked questions

Why one letter instead of two, like British references?

Ireland fits inside a single 500 km grid zone, so one letter names the 100 km square — J for Belfast's square, O for Dublin's, W for Cork's. British references need two letters because the National Grid spans several 500 km zones. The figures behave identically in both systems.

Which should I give someone — Irish Grid or ITM?

Match the map they're holding. Paper OSNI/OSi maps, guidebooks and mountain rescue work in Irish Grid letters; GIS software, surveyors and official digital data want ITM. This tool shows both at once, so read out whichever the other side expects — a 6-figure Irish Grid reference is the safe default for people.

Does it work in the Republic of Ireland too?

Yes — the Irish Grid and ITM cover the whole island as one seamless system; there is no separate northern or southern grid. What it doesn't cover is Great Britain, which uses the OS National Grid — a different datum and lettering scheme with its own page here.

How accurate is the conversion?

Irish Grid: within a few meters, using the standard published Helmert transformation between GPS's WGS84 and the 1965 Irish datum — well inside a 6- or 8-figure square. ITM: essentially GPS-accurate, since its ETRS89 datum agrees with WGS84 to under a meter. Survey-grade work should use OSi/OSNI's official tools.

Does this page work offline in the hills?

Yes. The mathematics runs entirely on your device and the page is cached after your first visit — finding and converting references needs no signal. Only the optional map display and place-name search require a connection.