C: Converting between grid eastings & northings and ellipsoidal coordinates

Please note this page is no longer updated. For the latest version download the pdf.

PDF showing the equations used to convert between these type of coordinates and a worked example.

Please note: these formulae are used to convert the format of coordinates between grid eastings and northings and ellipsoidal coordinates (latitude and longitude) on the same datum. This is not a transformation. If you need to transform between GPS coordinates and OSGB36 National Grid coordinates, you need to apply either the OSTN02 transformation (see 6.3) or the approximate Helmert type transformation (see 6.6).

Ellipsoid and projection constants commonly used in the UK can be found within annexe A.