Addrova

Convert Lambert 93 to GPS (WGS84)

French public datasets often give coordinates in Lambert 93 (EPSG:2154), in metres, while web maps and GPS use WGS84 (EPSG:4326), in degrees. This page shows how to convert between the two.

In your browser

Use the coordinate converter. It also handles UTM and degrees-minutes-seconds. The calculation runs in your browser; no coordinate is sent anywhere.

What the two systems are

  • WGS84 (EPSG:4326): latitude and longitude in decimal degrees. This is what the Addrova API returns, and what GPS devices use.
  • Lambert 93 (EPSG:2154): the official conic projection of metropolitan France. X (easting) and Y (northing) are in metres. The projection origin, 3°E and 46.5°N, is at X = 700,000 m and Y = 6,600,000 m.

Always check the order of the axes: in Lambert 93 you write X then Y (easting then northing); in WGS84 libraries differ, and many expect longitude then latitude.

A worked example

Central Paris, at latitude 48.8566 and longitude 2.3522, is at about X = 652,469.02 m and Y = 6,862,035.26 m in Lambert 93. Converting those two numbers back gives the original degrees.

Python

from pyproj import Transformer

to_wgs84 = Transformer.from_crs("EPSG:2154", "EPSG:4326", always_xy=True)
lon, lat = to_wgs84.transform(652469.02, 6862035.26)
print(lat, lon)   # about 48.8566, 2.3522

always_xy=True fixes the order to (X, Y) in and (longitude, latitude) out.

JavaScript

import proj4 from "proj4";

proj4.defs(
  "EPSG:2154",
  "+proj=lcc +lat_0=46.5 +lon_0=3 +lat_1=49 +lat_2=44 +x_0=700000 +y_0=6600000 +ellps=GRS80 +units=m +no_defs",
);
const [lon, lat] = proj4("EPSG:2154", "EPSG:4326", [652469.02, 6862035.26]);

The datum caveat

Lambert 93 is based on the RGF93 datum. WGS84 and RGF93 differ by about a metre. For mapping and address work that difference is negligible and the conversions above ignore it. For centimetre-level surveying, use a transformation grid published by the national mapping agency (IGN).

Overseas territories

Lambert 93 is for metropolitan France. Overseas territories use their own projections, and Corsica is covered by Lambert 93. Check the right EPSG code for your data. [À VÉRIFIER : codes EPSG des territoires d'outre-mer]

FAQ

Is the Lambert 93 to GPS conversion exact? The projection maths is exact; the datum difference of about one metre is the only simplification.

Does the Addrova API return Lambert 93? No. It returns WGS84 latitude and longitude. Convert with the tool above or with the code on this page.