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Coordinates

OS grid reference finder

Grid references like “TQ 302 796” are the ones on Ordnance Survey maps. Tap a point or search for a place to get its 6-, 8- and 10-figure reference and its easting and northing, or type a reference to see where it is.

By the All Map Tools Team

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Tap anywhere in Great Britain or Ireland. The point’s 100 km square is outlined with its letters.

Tap the map, search a place or type a reference.

How to read a grid reference

The British National Grid splits Great Britain into 100 km squares, each with two letters: the first is a large 500 km square (S, T, N, O or H) and the second is the 100 km square inside it. Then come the easting figures and the northing figures, always the same number of each, measured from the square’s south-west corner.

The more figures, the smaller the square. Here’s Big Ben, the example:

Big Ben’s grid reference with more or fewer figures
FiguresReferenceSquare
Letters onlyTQ100 km
2 figuresTQ 3 710 km
4 figuresTQ 30 791 km
6 figuresTQ 302 796100 m
8 figuresTQ 3026 796410 m
10 figuresTQ 30266 796431 m

Figures are cut off, never rounded: a reference names the square the point is in, and its south-west corner is the one with those numbers. So “TQ 302 796” isn’t a point but a 100 × 100 m square; type it in here and the map marks its center.

Northern Ireland and the Irish Grid

Northern Ireland doesn’t use the British National Grid. OSNI maps, and maps of the Republic from before 2001, use the Irish Grid: 100 km squares with a single letter, A to Z without I, with V in the south-west corner. Central Dublin, for example, is at “O 158 346”.

Tap anywhere on the island of Ireland and you get its Irish Grid reference plus its ITM coordinates, the grid now used across the whole island. The Irish Grid sits on the TM75 datum and is converted with OSi and OSNI’s official polynomial (EPSG:1041), accurate to about 0.4 m.

Why other tools give a different reference

GPS and Google Maps give coordinates in WGS84, while the National Grid sits on OSGB36, a datum from 1936. The two are up to about 120 m apart, and the gap changes from place to place. Ordnance Survey publishes an official transformation, OSTN15, that corrects it point by point with a grid of almost a million nodes.

This finder uses OSTN15, the same one QGIS and PROJ use, and matches Ordnance Survey’s 40 official test points within about 7 mm. Tools that project GPS coordinates without changing the datum end up around 100 m out: for Big Ben, one well-known site gives TQ 30155 79698, 125 m from the real spot.

Tips

  • Eastings before northings. On the map, read across first and then up: “along the corridor, then up the stairs.”
  • Six figures are enough to meet on a hill. A 100 m square is easy to see on a 1:25,000 map and to find on the ground; ten figures pin down a single post or trig point.
  • The letters matter. “302 796” without letters repeats in every 100 km square: without them, the reference could be anywhere in Great Britain.
  • Your GPS can show them too. Most hiking GPS units and British mapping apps let you pick “British National Grid” or “OSGB” as the position format and read the reference directly.
  • For many references at once, or to convert them to UTM or latitude and longitude in bulk, use the national grid converter: it reads whole lists and exports a CSV.

Frequently asked questions

How do I find a six-figure grid reference?

Tap the point on the map or search for the place: you get the 6-figure reference (“TQ 302 796”) along with the 8- and 10-figure ones, each with a button to copy it.

Can I convert a grid reference to latitude and longitude?

Yes. Type it in the grid reference box, with letters (“SU 123 456”) or as an easting and northing (“412300 145600”), and you’ll see the point on the map with its WGS84 latitude and longitude.

Does it work in Northern Ireland?

Yes, with the Irish Grid used on OSNI maps: anywhere on the island of Ireland you get that one-letter reference plus ITM coordinates. You can also type an Irish reference, such as “J 338 740”.

Why does my GPS app show a different reference?

If it’s off by one in the last figure, it probably rounds instead of cutting off. If it’s about 100 m out, it doesn’t convert from WGS84 to OSGB36 with OSTN15, the official transformation this finder uses.

Do my coordinates leave my computer?

Not for the math: the reference is worked out in your browser, which only downloads the map and the piece of Ordnance Survey’s grid it needs (about 25 KB). If you search for a place by name, the search runs on our own gazetteer and, if that finds nothing, on Photon.

Related tools

All tools
National grid converter Convert coordinates to and from each country’s official grid, such as ETRS89, Lambert-93 or Gauss-Krüger. Address to coordinates Turn addresses into latitude and longitude, one at a time or in a batch you can download as CSV. UTM to latitude and longitude Turn a UTM zone, easting and northing into latitude and longitude, and see the point on the map. Coordinates to address Paste a latitude and longitude and get the nearest street address, with the point marked on the map. Coordinate converter Convert coordinates between decimal degrees, DMS, UTM, MGRS, geohash and Plus Codes in one go. Coordinates to city Find which city or town a pair of coordinates falls in, along with its region and country.

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