Free, no sign-up, runs in your browser. Convert Web Mercator coordinates to latitude and longitude, or the other way round, one pair or a whole list at a time.
261845.71, 6250564.35 -8238310.24, 4970071.58
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Open the map editorEPSG:4326 is the WGS84 coordinate system most people know: latitude and longitude in degrees, as used by GPS and GeoJSON. EPSG:3857, usually called Web Mercator, is the projected system behind most web map tiles. Its coordinates are X and Y distances in metres from the point where the equator meets the prime meridian.
Choose a direction, then paste one pair per line. For 4326 to 3857, enter latitude first, then longitude, for example 48.8566, 2.3522. For 3857 to 4326, enter X then Y in metres. Commas, spaces, or tabs between the two numbers all work. Lines that cannot be read, or that fall outside the valid range, are listed under the box with their line number, while the valid lines still convert.
Web Mercator stretches toward the poles and is undefined at the poles themselves, so latitudes are limited to about ±85.0511°. The matching X and Y limits are roughly ±20,037,508 metres. The converter uses the spherical formulas with the WGS84 equatorial radius of 6,378,137 metres, which is exactly how EPSG:3857 is defined.
You will run into 3857 when a web mapping library, tile server, or exported dataset reports huge numbers like -8238310, 4970072 where you expected degrees. Convert them here to get coordinates you can drop into a spreadsheet, GeoJSON file, or map. Use the copy button for plain text or the CSV button for a file with a header row. Everything is computed locally, so your coordinates never leave your device.