Convert coordinates from OSGB36 (EPSG:4277) to WGS 84 (EPSG:4326) — official EPSG transformation parameters, accuracy and area of use, with a free in-browser converter.
OSGB36 (EPSG:4277) is Great Britain's classical datum on the Airy 1830 ellipsoid, realised through the retriangulation of 1936–1953. It underlies the Ordnance Survey National Grid (EPSG:27700) — so almost any British easting/northing ultimately ties back to it.
The simple Helmert transformations published by EPSG are accurate to a few metres at best, because OSGB36 contains regional distortions that no seven-parameter fit can capture. Ordnance Survey's official answer is the OSTN15 grid transformation, which reproduces the true relationship to about 0.1 m.
Use the Helmert for mapping and visualisation; use OSTN15 (in PROJ, QGIS or OS tools) whenever you need survey-grade results in Britain.
Try it: Big Ben, London
Input (EPSG:4277): -0.1246, 51.5007
The EPSG Geodetic Parameter Dataset defines 9 transformations between OSGB36 (EPSG:4277) and WGS 84 (EPSG:4326). Each applies to a specific area — pick the one whose area of use covers your data.
Grid file: OSTN02_NTv2.gsb
Parameter values taken from OSGB36 to ETRS89 (1) (tfm code 5338) assuming that ETRS89 is coincident with WGS 84 within the accuracy of the tfm.
Grid file: OSTN15_NTv2_OSGBtoETRS.gsb
Parameter values taken from OSGB36 to ETRS89 (2) (tfm code 7709) assuming that ETRS89 is coincident with WGS 84 within the accuracy of the tfm. Replaces OSGB36 to WGS 84 (7) (tfm code 5339).
| Parameter | Value | Unit |
|---|---|---|
| X-axis translation(tx) | 446.448 | metre |
| Y-axis translation(ty) | -125.157 | metre |
| Z-axis translation(tz) | 542.06 | metre |
| X-axis rotation(rx) | 0.15 | arc-second |
| Y-axis rotation(ry) | 0.247 | arc-second |
| Z-axis rotation(rz) | 0.842 | arc-second |
| Scale difference(ds) | -20.489 | parts per million |
Commonly referred to as the "OSGB Petroleum transformation". For a more accurate transformation see ETRS89 to OSGB36 / British National Grid (3) (code 7953).
| Parameter | Value | Unit |
|---|---|---|
| X-axis translation(tx) | 370.936 | metre |
| Y-axis translation(ty) | -108.938 | metre |
| Z-axis translation(tz) | 435.682 | metre |
Derived by CGG for 1994 3D seismic survey.
| Parameter | Value | Unit |
|---|---|---|
| X-axis translation(tx) | 371 | metre |
| Y-axis translation(ty) | -112 | metre |
| Z-axis translation(tz) | 434 | metre |
Derived at 24 stations. Accuracy 5m, 5m and 6m in X, Y and Z axes.
| Parameter | Value | Unit |
|---|---|---|
| X-axis translation(tx) | 384 | metre |
| Y-axis translation(ty) | -111 | metre |
| Z-axis translation(tz) | 425 | metre |
Derived at 13 stations. Accuracy 10m in each axis.
| Parameter | Value | Unit |
|---|---|---|
| X-axis translation(tx) | 375 | metre |
| Y-axis translation(ty) | -111 | metre |
| Z-axis translation(tz) | 431 | metre |
Derived at 38 stations. Accuracy 10m, 10m and 15m in X, Y and Z axes.
| Parameter | Value | Unit |
|---|---|---|
| X-axis translation(tx) | 371 | metre |
| Y-axis translation(ty) | -111 | metre |
| Z-axis translation(tz) | 434 | metre |
Derived at 25 stations. Accuracy 10m, 10m and 15m in X, Y and Z axes.
| Parameter | Value | Unit |
|---|---|---|
| X-axis translation(tx) | 370 | metre |
| Y-axis translation(ty) | -108 | metre |
| Z-axis translation(tz) | 434 | metre |
Derived at 3 stations. Accuracy 20m in each axis.
The same transformation with common GIS tools and libraries:
from pyproj import Transformer
transformer = Transformer.from_crs("EPSG:4277", "EPSG:4326", always_xy=True)
x, y = transformer.transform(-73.9857, 40.7484)
print(x, y)geographic system using latitude and longitude on an ellipsoid · Area of use: UK - Britain and UKCS 49°45'N to 61°N, 9°W to 2°E
+proj=longlat +ellps=airy +no_defs +type=crsMore about EPSG:4277 →
geographic system using latitude and longitude on an ellipsoid · Area of use: World (by country)
+proj=longlat +datum=WGS84 +no_defs +type=crsMore about EPSG:4326 →