GetTheData (BNG Converter) API

Free British National Grid conversion API with no key: turn OSGB36 easting and northing into WGS84 latitude and longitude, plus UK postcode lookup. Tested example included.

No API key requiredCORS enabledHTTPSFree tier

Endpoint tested and returned HTTP 200 on 2026-08-21

What is the GetTheData (BNG Converter) API?

GetTheData's bng2latlong endpoint is a free, key-free API that converts British National Grid coordinates — OSGB36 easting and northing — into WGS84 latitude and longitude. The same host also offers UK postcode and address lookups on the same key-free terms.

Anyone working with British public data hits this problem early. Ordnance Survey products, Environment Agency datasets, planning records and most local authority exports are published in the British National Grid: a pair of metre values like 389490, 244550 that no web mapping library understands. Converting them properly means a datum shift from OSGB36 to WGS84, not just a projection change, and the naive approximations are out by several metres.

This endpoint does the full transformation and returns a plain object with `status`, the echoed easting and northing, and the resulting latitude and longitude. Two practical notes: the result is rounded to five decimal places, which is roughly a metre and entirely adequate for the input precision, and the parameters go in the path rather than the query string, so the URL is `/bng2latlong/{easting}/{northing}` with no question mark in sight.

Quick facts

Base URL: https://api.getthedata.com
Authentication: No key or account for the conversion and postcode endpoints. The operator asks for attribution when the data is republished.
Rate limit: No published numeric quota. Fair use is expected; batch conversions should be spaced or done locally with a projection library.
Pricing: Free.
CORS: Enabled — callable directly from browser JavaScript
Official docs: Read the docs

How to use the GetTheData (BNG Converter) API

Every request below was executed against the live API on 2026-08-21, and the response shown is the real body it returned — not an illustration.

1. Convert a British National Grid reference to latitude and longitude

GET https://api.getthedata.com/bng2latlong/389490/244550

curl

curl 'https://api.getthedata.com/bng2latlong/389490/244550'

JavaScript (fetch)

const res = await fetch("https://api.getthedata.com/bng2latlong/389490/244550");
if (!res.ok) throw new Error(`Request failed: ${res.status}`);
const data = await res.json();
console.log(data);

Python (requests)

import requests

res = requests.get("https://api.getthedata.com/bng2latlong/389490/244550", timeout=20)
res.raise_for_status()
print(res.json())

Response — HTTP 200

{
  "status": "ok",
  "easting": 389490,
  "northing": 244550,
  "latitude": 52.09918,
  "longitude": -2.15485
}

Parameters

Parameter	Type	Required	Description
`easting`	path	Required	OSGB36 easting in metres. Six digits for most of Great Britain. `389490`
`northing`	path	Required	OSGB36 northing in metres. `244550`
`(postcode)`	path	Optional	`/postcode/{postcode}` returns coordinates and administrative geography for a UK postcode. `SW1A2AA`
`(latlong2bng)`	path	Optional	`/latlong2bng/{lat}/{long}` performs the reverse conversion back into the grid. `52.09918`

Response fields

statusstring: "ok" on success, or "error" with a message when the input is out of range.
easting / northinginteger: The values you supplied, echoed back so a batch of responses can be matched to its inputs.
latitudefloat: WGS84 latitude in decimal degrees, rounded to five places — about one metre.
longitudefloat: WGS84 longitude in decimal degrees, negative west of Greenwich.

What you can build with the GetTheData (BNG Converter) API

Plot Ordnance Survey or Environment Agency data on a web map
Convert a council or planning dataset from BNG to WGS84 for analysis
Reconcile a legacy grid-referenced asset register with GPS coordinates
Check a projection library's output against an independent implementation
Convert UK postcodes to coordinates using the sibling endpoint

Common errors and how to fix them

status is "error"

The easting or northing falls outside the British National Grid.

Fix: Valid eastings run roughly 0 to 700000 and northings 0 to 1300000. Values outside that are usually a swapped pair or a different projection entirely.

The point lands in the sea

Easting and northing were passed in the wrong order.

Fix: Easting comes first and is the smaller of the two across most of Britain. Swapping them typically throws the result into the North Sea.

Result differs from a local library by several metres

OSGB36 to WGS84 is a datum shift, and implementations use different transformation grids.

Fix: A difference of a few metres between the simple Helmert transformation and OSTN15 is expected. Match the method to the precision your source data actually has.

404 on the postcode endpoint

The postcode contains a space or is not a current UK postcode.

Fix: Strip spaces before sending. Terminated postcodes are not in the dataset even though they were once valid.

GetTheData (BNG Converter) API — frequently asked questions

Is the BNG conversion API free?

Yes, free with no key or registration. The operator asks for attribution if you republish the data, which is a reasonable ask for a service run without charge.

What is the British National Grid?

It is the projected coordinate system Ordnance Survey uses for Great Britain, expressing positions as easting and northing in metres from a false origin south-west of the Scilly Isles. Nearly all British public geodata is published in it.

How accurate is the conversion?

Results are given to five decimal places, roughly a metre, which matches the precision of a metre-resolution grid reference. Different transformation methods can disagree by a couple of metres, so do not read more precision into the output than the input carried.

Can it convert in the other direction?

Yes. The `/latlong2bng/{lat}/{long}` endpoint takes WGS84 degrees and returns the corresponding British National Grid easting and northing.

Tools that pair with this API

Coordinate Converter

Convert GPS coordinates between decimal degrees, degrees-minutes-seconds and decimal minutes instantly. Paste any format like 40°26'46"N and copy the result.

UTM Coordinate Converter

Convert latitude and longitude to UTM zone, easting and northing on WGS-84 — and convert UTM grid references back to lat/long. Free and offline.

Decimal to DMS Converter

Convert decimal degrees to degrees, minutes and seconds. Choose the seconds precision, see the component breakdown and bulk-convert a whole list.

GetTheData (BNG Converter) is an independent third-party service and is not affiliated with ByteTools or ByteVancer. Details on this page were verified on 2026-08-21; always check the official documentation before relying on this API in production, as terms and limits can change.