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EPSG:27700 — OSGB36 / British National Grid

British National Grid — the projected CRS used by every Ordnance Survey product and the Land Registry.

Code
EPSG:27700
Type
Projected
Area
UK - Britain and UKCS 49°45'N to 61°N, 9°W to 2°E

PROJ definition

+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +units=m +no_defs +type=crs

Geographic bounds

W -9.01°   S 49.75°   E 2.01°   N 61.01°

Convert coordinates with EPSG:27700

About EPSG:27700

EPSG:27700 is the OSGB36 / British National Grid: a Transverse Mercator projection of the OSGB36 datum (Airy 1830 ellipsoid), with central meridian 2°W, latitude of origin 49°N, false easting 400 km, false northing −100 km, and scale factor 0.9996012717. Eastings and northings are in metres, ranging across Great Britain from roughly (0, 0) at the south-west to (700,000, 1,300,000) in the Shetlands.

Ordnance Survey adopts the alphanumeric grid reference (e.g. SU 387 148) as its public-facing format; each two-letter prefix denotes a 100 km square. The numeric easting/northing form is what this converter uses.

The OSGB36 datum differs from WGS 84 by tens of metres because Airy 1830 was tuned for the British Isles. Accurate conversion to/from WGS 84 requires the OSTN15 grid-shift transformation; a simple Helmert seven-parameter approximation introduces around 5 m of error and is not suitable for surveying.

Common use cases

  • All Ordnance Survey mapping (OS Maps, OS OpenData, OS MasterMap)
  • UK Land Registry and conveyancing records
  • Defra / Natural England environmental datasets
  • Local authority planning and asset systems

Common transformations from EPSG:27700

Frequently asked questions

What's the difference between EPSG:27700 and EPSG:4277?
EPSG:4277 is the geographic OSGB 1936 lat/lon datum; EPSG:27700 is its Transverse Mercator projection that produces the familiar eastings and northings.
Why is my BNG result a few metres off from the OS web tool?
Most browser-based converters (this one included) approximate the OSGB36 ↔ WGS 84 transformation with Helmert parameters. The Ordnance Survey OSTN15 grid-shift gives sub-metre accuracy and is required for surveying-grade work.
What is the proj4 string for EPSG:27700?
The proj4 definition for EPSG:27700 is: +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +units=m +no_defs +type=crs
Where is EPSG:27700 used?
EPSG:27700 (OSGB36 / British National Grid) is defined for the area: UK - Britain and UKCS 49°45'N to 61°N, 9°W to 2°E.