Free tool
Grid reference converter
Turn an Ordnance Survey or Irish grid reference into latitude and longitude, or the other way round, at 6, 8 or 10 figures.
Open in Apple Maps · Google Maps
How precise is a grid reference?
| Figures | Example | Square | Good for |
|---|---|---|---|
| 6 | SO 479 590 | 100 m | A rough location only |
| 8 | SO 4792 5901 | 10 m | The minimum the Portable Antiquities Scheme asks for |
| 10 | SO 47925 59012 | 1 m | Best, from a GPS fix where the find came up |
The two letters name a 100 km square of the National Grid (one letter on the Irish Grid). The figures are eastings then northings within it, so "SO 479 590" means 47.9 km east and 59.0 km north of the south-west corner of square SO.
Keep precise findspots to yourself, the landowner and your Finds Liaison Officer: published locations can draw nighthawks (illegal detectorists). Recording rules for each country are on detecting laws by country.
Questions
What precision does the Portable Antiquities Scheme need?
At least an 8-figure grid reference (a 10 m square), ideally 10 figures from GPS. The PAS never shows precise findspots publicly: the public sees only the parish.
Why does a grid reference name a square rather than a point?
Each grid reference is the square the point lies in: a 6-figure reference is a 100 m square, 8 figures a 10 m square and 10 figures a 1 m square. Converting a reference back to latitude and longitude gives the centre of that square.
Which grid should I use in Northern Ireland?
The Irish Grid, which covers the whole island of Ireland. The converter picks it automatically for locations in Ireland and Northern Ireland, and the Ordnance Survey National Grid for Great Britain and the Isle of Man.
Does my location leave my device?
No. The conversion runs in your browser, and if you choose Use my location, your browser shares it with this page only. Nothing is sent to a server.