Go to Field En Maps Co-ordinante Converter (see Resources). Find the "Great Britain National Grid" section, located on the left hand side right below the "Geodetic Co-ordinates" section. Enter in your National Grid eastings and northings number, then press "Convert." The rest of the numbers on the page will change to reflect that location.
Download the National Grid Calculator (see Resources). The program is free to download as of February 2011, and will convert the national grid and ordinance survey to longitude and latitude co-ordinates.
Go to Moveable Type (see Resources). Type your Ordinance Survey number into the box that says "OS Grid Ref" and press "Enter." The longitude and latitude co-ordinates will change to correspond with the OS reference number. This program is free to use as of February 2011.
