Source: EPSG:4326 — WGS 84
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 →
Convert EPSG:4326 to EPSG:27700
Online coordinate converter from WGS 84 (EPSG:4326) to OSGB36 / British National Grid (EPSG:27700). Enter your source coordinates and get the result instantly. All transformations happen in your browser — no data is sent to any server.
About converting WGS 84 to OSGB36 / British National Grid
Converting from WGS 84 (EPSG:4326) to British National Grid (EPSG:27700) is the standard transformation for putting GPS data onto Ordnance Survey maps. The result is eastings and northings in metres on the OSGB36 datum, ranging from (0,0) at the south-west to about (700,000, 1,300,000) in the Shetlands.
The transformation involves both a projection change (Transverse Mercator) and a datum shift from WGS 84 to OSGB36, since OSGB36 was built on the Airy 1830 ellipsoid tuned for the British Isles. Helmert seven-parameter approximations give about 5 m accuracy across Great Britain. The Ordnance Survey's official OSTN15 grid-shift transformation gives sub-metre accuracy and is required for surveying-grade work — it cannot run in a browser without bundling the grid file.
For visual or sub-metre-tolerant work the result will match OS Maps to a few metres. For legal, cadastral or surveying applications use OS's official conversion service or a desktop GIS with OSTN15 installed.
Why people convert EPSG:4326 to EPSG:27700
- Plotting GPS readings onto Ordnance Survey OS Maps
- Aligning external data with UK Land Registry boundaries
- Converting GPX tracks into BNG eastings/northings
- Imports into UK local-authority GIS systems
Try it: Big Ben, London
Input (EPSG:4326): -0.1247, 51.5007
Convert EPSG:4326 to EPSG:27700 in code
The same transformation with common GIS tools and libraries:
from pyproj import Transformer
transformer = Transformer.from_crs("EPSG:4326", "EPSG:27700", always_xy=True)
x, y = transformer.transform(-73.9857, 40.7484)
print(x, y)Target: EPSG:27700 — OSGB36 / British National Grid
projected system measured in linear units (typically metres) · Area of use: UK - Britain and UKCS 49°45'N to 61°N, 9°W to 2°E
+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +units=m +no_defs +type=crsMore about EPSG:27700 →
Frequently asked questions
- Why is my BNG result a few metres off from the OS web converter?
- OS uses the OSTN15 grid-shift transformation, which is sub-metre accurate but requires a 4 MB grid file. Browser tools (this one included) approximate the OSGB36 ↔ WGS 84 step with Helmert parameters, introducing 1-5 m of error.
- Can I use this for property boundaries or surveying?
- No — for legal or surveying-grade work use the Ordnance Survey's official conversion service or a GIS package configured with OSTN15.
- How accurate is converting WGS 84 to OSGB36 / British National Grid?
- Projection-only conversions are accurate to floating-point precision. If a datum shift is involved, browser-based tools use Helmert parameters which are accurate to roughly 1-5 m; for surveying-grade work apply the official grid-shift transformation in a desktop GIS.
- Does my data leave the browser when I use this converter?
- No. All coordinate transformations are computed locally in your browser using proj4js. The coordinates you enter are never transmitted to any server.