British National Grid (OSGB36) Converter
A free, browser-based converter. Runs entirely in your browser — no sign up, nothing stored.
British National Grid (OSGB36 / EPSG:27700)
Convert in either direction.
Result
Enter a coordinate and press Convert.
How to use this calculator
- Pick the direction — latitude/longitude to grid, or grid to lat/long.
- Enter the coordinates (decimal degrees, or easting/northing in metres).
- Press Convert to read the result in the other system.
How it works
Converts between WGS84 latitude/longitude and the British National Grid (OSGB36, EPSG:27700) using a Transverse Mercator projection and a 7-parameter datum shift.
The datum shift is accurate to a few metres. For survey-grade work use the official OSTN15 grid-shift transformation instead.
Worked example
London (51.5074, −0.1278). Converts to roughly 530,034 m E, 180,382 m N on the British National Grid.
Frequently asked questions
How accurate is the conversion?
It is good to a few metres because it uses a 7-parameter Helmert datum shift. Centimetre-level work needs the official OSTN15 grid file.
Is the input WGS84 or OSGB36?
Latitude/longitude is treated as WGS84 (what GPS and phones report). Eastings/northings are OSGB36 British National Grid metres.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.