Convert coordinates from OSGB36 (EPSG:4277) to ETRS89 (EPSG:4258) — official EPSG transformation parameters, accuracy and area of use, with a free in-browser converter.
The EPSG Geodetic Parameter Dataset defines 2 transformations between OSGB36 (EPSG:4277) and ETRS89 (EPSG:4258). Each applies to a specific area — pick the one whose area of use covers your data.
Grid file: OSTN02_NTv2.gsb
Approximate alternative to official OSTN02 method (tfm code 7952). Accuracy at 2000 test points compared to OSTN02 (tfm code 1039): latitude 0.5mm av, 17mm max; longitude 0.8mm av, 23mm max. May be taken as approximate CT to WGS 84 - see code 5339.
Grid file: OSTN15_NTv2_OSGBtoETRS.gsb
Approximate alternative to official OSTN15 method (tfm code 7953). May be taken as approximate transformation OSGB36 to WGS 84 - see code 7710. Replaces OSGB36 to ETRS89 (1) (tfm code 5338).
The same transformation with common GIS tools and libraries:
from pyproj import Transformer
transformer = Transformer.from_crs("EPSG:4277", "EPSG:4258", 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: Europe - ETRF by country
+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs +type=crsMore about EPSG:4258 →