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British National Grid converter

Enter OS eastings and northings (e.g. 530047 179640) to get latitude and longitude, or the reverse.

Read as: British National Grid (OSGB36)
  • Decimal degreesWGS 84 51.500729, -0.124625
  • Degrees, minutes, secondsWGS 84 51°30′02.62″N 0°07′28.65″W
  • Degrees, decimal minutesWGS 84 51°30.0437′N 0°07.4775′W
  • UTMWGS 84 30U 699566 5709431
  • MGRS / USNGWGS 84 30U XC 99565 09430
  • British National Grid (OSGB36)TQ 30266 79643 · EPSG:27700 · ±0.03 m 530266.35 179643.71
  • Plus CodeOpen Location Code 9C3XGV2G+75
  • Geohash gcpuvpmm2
  • Maidenheadham radio IO91wm

Tap the map to convert that point.

The British National Grid

The Ordnance Survey National Grid (EPSG:27700) is the coordinate system of every OS map of Great Britain. It is a Transverse Mercator projection of the OSGB36 datum on the Airy 1830 ellipsoid, with a false origin south-west of the Isles of Scilly so all eastings and northings are positive.

GPS gives coordinates in ETRS89 / WGS 84, which differ from OSGB36 by up to about 120 m. This converter uses OSTN15, Ordnance Survey's definitive transformation grid, and reproduces the official OSTN15 test points to within 1 cm. The grid is downloaded only when your point is in Great Britain; if it cannot be loaded, the result falls back to OS's 7-parameter Helmert transformation (about 3.5 m) and the accuracy shown next to it changes to match.

Frequently asked questions

How accurate is the conversion to grid references?

To within about 1 cm of Ordnance Survey's own OSTN15 results, anywhere in Great Britain. OSTN15 is the definitive transformation between ETRS89 and the National Grid. A plain GPS fix is in WGS 84, which today differs from ETRS89 by under 1 m, so for survey work start from ETRS89 coordinates (for example from OS Net).

Does it accept letter grid references like TQ 30047 79640?

Yes. Type TQ 30047 79640, TQ3004779640 or a shorter reference such as TQ 300 796 (100 m). The result also shows the letter reference next to the full numeric easting and northing.

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