OS Transform API

Convert between British National Grid coordinates, Grid References, and WGS84 Lat/Lng

About this API

This free API provides coordinate transformations between OSGB36/British National Grid (EPSG:27700) and WGS84 (EPSG:4326). It uses proj4js with the standard grid based datum adjustments to provide best in class accuracy across Great Britain.

All endpoints support both GET (query parameters) and POST (JSON body) requests.

1. Easting/Northing → Lat/Lng

POST/GET /api/to-latlng
Example: 337297
Example: 503695
Default: 7

2. Lat/Lng → Easting/Northing

POST/GET /api/from-latlng
Example: 54.42480998
Example: -2.96793742
Default: 2

3. Easting/Northing → Grid Reference

POST/GET /api/to-gridref
Example: 337297
Example: 503695

4. Grid Reference → Easting/Northing

POST/GET /api/from-gridref
Example: NY 37297 03695

5. Grid Reference → Lat/Lng (Direct)

POST/GET /api/gridref-to-latlng
Example: NY 37297 03695
Default: 7