Please begin by selecting the area for which you wish to convert co-ordinates:
Co-ordinate Converter screenshot - Great Britain Great Britain (including Channel Is. & Isle of Man)
  • Latitude/Longitude (ETRS89) (GPS-compatible)
  • Latitude/Longitude (OSGB36)
  • Latitude/Longitude (ED50)
  • UTM Co-ordinates (ETRS89 or ED50) Zones 29/30/31
  • GB National Grid
  • GB National Yard Grid
  • Cassini Projection (Delamere origin)
  • War Office Cassini Grid
  • Bonne Projection (Scotland)
  • OS County Series Co-ordinates & Sheet References
Co-ordinate Converter screenshot - Ireland Ireland
  • Latitude/Longitude (ETRS89) (GPS-compatible)
  • Latitude/Longitude (OS Ireland 65)
  • Latitude/Longitude (ED50)
  • UTM Co-ordinates (ETRS89 or ED50) Zones 29/30
  • Irish National Grid
  • Irish Transverse Mercator Grid
  • Bonne Projection (Ireland)
  • War Office Irish Grid
OSTN02 and OSi/OSNI Polynomial enabled


If you find Co-ordinate Converter useful and would like to make a donation for the work that has gone into making it - or for the upkeep of this website - please use the PayPal link to the left. Please note that this is not compulsory - Co-ordinate Converter is free for non-commercial use.
Interested in using Co-ordinate Converter functions on your own site?

Co-ordinate Converter is written in JavaScript and as such could be the ideal tool for your web-based application. Fully-comprehensive API documentation is available as a PDF file: cconv_api_1-2-003.pdf

Please note that use of the Co-ordinate Converter API is free for non-commercial purposes only. If you wish to use it for a commercial application please contact me for details and pricing. Usage of the Co-ordinate Converter API is monitored.

What is Co-ordinate Converter?

Co-ordinate Converter grew out of a practical need to convert between the projection co-ordinates used to construct Ordnance Survey small-scale maps of Great Britain from the early 20th century and the modern-day GB National Grid.

It began life in the Summer of 2004 as a very simple piece of software - written in Visual Basic - allowing three-way conversion between OS Latitude/Longitude, GB National Grid and Cassini (Delamere) co-ordinates. From there the software grew to include support for conversions to/from other projected co-ordinate systems commonly in use in Great Britain and Ireland.

In November 2007 the County Series sheet references for Great Britain and the Isle of Man were incorporated into the software, introducing a new level of versatility to Co-ordinate Converter.

Between December 2008 and April 2009 the software version was ported to the current web-based version, including support for additional co-ordinate systems, and for the first time conversion to/from GPS-compatible latitude/longitude for Great Britain and Ireland. Details can be found in the Co-ordinate Converter Version History.

Please note that the downloadable standalone version of Co-ordinate Converter is currently not available pending a completely revised version (no release date has yet been set).

Legal notice

Co-ordinate Converter is copyright 2004-2009 Ed Fielden.
You may use Co-ordinate Converter for non-commercial use only, except by prior agreement.
While great care has been taken in development and testing, the results of transformations provided by Co-ordinate Converter should not be relied upon for critical applications. No liability can be accepted for any loss or damage - direct or consequential - arising from the use of Co-ordinate Converter.

Any comments, suggestions, or error reports? Get in touch.

Page last updated: 24 April 2012