This tool provides high-precision, bidirectional coordinate transformations between three major UK survey grids:

• OSGB36: The familiar Ordnance Survey National Grid.
• ETRS89: The standard GPS-compatible system for Europe (effectively WGS84).
• LSG 2025: The London Survey Grid, used for major infrastructure projects.

The transformations are based on the official OSTN15 model from Ordnance Survey and the 7-parameter Helmert transformation specified by Transport for London for the LSG (2025).

Please consult the Transport for London Lead Surveyor for more information on LSG.

This tool has been built using the following resources:

Ordnance Survey Developer Resources

Transport for London Standard S1026 (A4) Topographic Surveys and Mapping

This tool is still under development. Use with caution and check all results before use.