EPSG Library · Europe

EPSG:27700 — OSGB36 / British National Grid

Source: EPSG Dataset via PROJ 9.5.1 · Updated 2026-10-05

Summary

EPSG:27700 (OSGB36 / British National Grid) is a projected coordinate reference system on the Ordnance Survey of Great Britain 1936 datum using the Transverse Mercator method, with coordinates in metres. Area of use: United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland).

Type: projected
Datum: Ordnance Survey of Great Britain 1936
Units: metre
Axes: E, N

Definition

EPSG:27700 as published in the EPSG Dataset (PROJ 9.5.1).
Property	Value
EPSG code	EPSG:27700
Name	OSGB36 / British National Grid
Type	Projected CRS
Datum	Ordnance Survey of Great Britain 1936
Ellipsoid	Airy 1830 (a = 6,377,563.396 m, 1/f = 299.324965)
Prime meridian	Greenwich
Projection method	Transverse Mercator
Axes	Easting (E, east, metre); Northing (N, north, metre)
Scope	Engineering survey, topographic mapping.
Bounding box	-9.01° to 2.01° longitude, 49.75° to 61.01° latitude

Area of use

United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland). Isle of Man onshore.

Projection parameters

Transverse Mercator parameters.
Parameter	Value	Unit
Latitude of natural origin	49	degree
Longitude of natural origin	-2	degree
Scale factor at natural origin	0.9996012717	unity
False easting	400,000	metre
False northing	-100,000	metre

Example coordinates

A WGS 84 point at longitude -3.5°, latitude 55.38° (inside the area of use) has these coordinates in EPSG:27700:

Computed with PROJ using the EPSG default operation: unavailable until proj_trans is called.
Axis	Value	Unit
E	305,055.406	m
N	610,582.448	m

At this point the projection scale factor is 0.99971207 and the grid convergence is -1.234499°.

Open this conversion in the coordinate converter

Transformations to WGS 84

Candidate operations from the EPSG Dataset, best first as ranked by PROJ.
Operation	Accuracy	Area of use
axis order change (2D) + OSGB36 to WGS 84 (6) + axis order change (2D)	2 m	United Kingdom (UK) - Great Britain - England and Wales onshore, Scotland onshore and Western Isles nearshore including Sea of the Hebrides and The Minch; Isle of Man onshore.
axis order change (2D) + OSGB36 to WGS 84 (1) + axis order change (2D)	21 m	United Kingdom (UK) - Great Britain - England and Wales onshore, Scotland onshore and Western Isles nearshore including Sea of the Hebrides and The Minch; Isle of Man onshore.
axis order change (2D) + OSGB36 to WGS 84 (2) + axis order change (2D)	10 m	United Kingdom (UK) - England onshore.
axis order change (2D) + OSGB36 to WGS 84 (3) + axis order change (2D)	21 m	United Kingdom (UK) - England and Wales; Isle of Man - onshore.
axis order change (2D) + OSGB36 to WGS 84 (4) + axis order change (2D)	18 m	United Kingdom (UK) - Scotland (including Orkney and Shetland Islands), onshore and nearshore.
axis order change (2D) + OSGB36 to WGS 84 (5) + axis order change (2D)	35 m	United Kingdom (UK) - Wales onshore.
axis order change (2D) + OSGB36 to WGS 84 (8) + axis order change (2D)	3 m	United Kingdom (UK) - Wytch Farm area - onshore and offshore.

Transformations change the datum, so each has an accuracy and an area of use. Choose the most accurate one that covers your data and record its name. See datum transformations.

Grid-based operations not bundled with standard PROJ installs: OSGB36 to WGS 84 (9).

Definitions and downloads

PROJ string

+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

A PROJ string cannot carry every EPSG detail (axis order, datum ensemble, transformations). Prefer WKT2 or the EPSG code itself.

Proj4js definition used by the converter

+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +units=m +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 +no_defs

Datum shift from OSGB36 to WGS 84 (6) (EPSG accuracy 2 m), the best single Helmert operation for this area of use. Where PROJ prefers a grid-based or multi-step operation (see the table above), results can differ by up to that operation's accuracy.

WKT2:2019

PROJCRS["OSGB36 / British National Grid", BASEGEOGCRS["OSGB36", DATUM["Ordnance Survey of Great Britain 1936", ELLIPSOID["Airy 1830",6377563.396,299.3249646, LENGTHUNIT["metre",1]]], PRIMEM["Greenwich",0, ANGLEUNIT["degree",0.0174532925199433]], ID["EPSG",4277]], CONVERSION["British National Grid", METHOD["Transverse Mercator", ID["EPSG",9807]], PARAMETER["Latitude of natural origin",49, ANGLEUNIT["degree",0.0174532925199433], ID["EPSG",8801]], PARAMETER["Longitude of natural origin",-2, ANGLEUNIT["degree",0.0174532925199433], ID["EPSG",8802]], PARAMETER["Scale factor at natural origin",0.9996012717, SCALEUNIT["unity",1], ID["EPSG",8805]], PARAMETER["False easting",400000, LENGTHUNIT["metre",1], ID["EPSG",8806]], PARAMETER["False northing",-100000, LENGTHUNIT["metre",1], ID["EPSG",8807]]], CS[Cartesian,2], AXIS["(E)",east, ORDER[1], LENGTHUNIT["metre",1]], AXIS["(N)",north, ORDER[2], LENGTHUNIT["metre",1]], USAGE[ SCOPE["Engineering survey, topographic mapping."], AREA["United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland). Isle of Man onshore."], BBOX[49.75,-9.01,61.01,2.01]], ID["EPSG",27700]]

Downloads

27700.prj — ESRI WKT for shapefiles
27700.wkt — OGC WKT2:2019

FAQ

What is EPSG:27700?

Where can EPSG:27700 be used?

Its area of use is: United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland). Isle of Man onshore.

Is EPSG:27700 in metres or degrees?

EPSG:27700 is projected, so coordinates are easting and northing in metres, not degrees.

How do I convert EPSG:27700 to latitude and longitude?

Transform from EPSG:27700 to EPSG:4326 (WGS 84). In GeoCAD Bridge open the coordinate converter with EPSG:27700 preselected, enter easting and northing, and choose WGS 84 as the target.

How accurate is the transformation from EPSG:27700 to WGS 84?

The most accurate EPSG transformation listed here is “axis order change (2D) + OSGB36 to WGS 84 (6) + axis order change (2D)”, with a stated accuracy of 2 m for United Kingdom (UK) - Great Britain - England and Wales onshore, Scotland onshore and Western Isles nearshore including Sea of the Hebrides and The Minch; Isle of Man onshore.. Always check the area of use before applying it.

Coordinate systems

Articles

Tools

References

IOGP. EPSG Geodetic Parameter Dataset, epsg.org/crs_27700.
PROJ 9.5.1 / pyproj 3.7.2, used to compute every value on this page.

Cite this page

GeoCAD Bridge. “EPSG:27700 — OSGB36 / British National Grid.” GeoCAD Bridge EPSG Library, updated 2026-10-05. https://www.geocadbridge.com/epsg/27700/