This question already has an answer here:

I need to extract the Lat/long coordinates of the centroids of districts. My QGIS project SCR and the different layers have all been set on "WGS 84 / UTM zone 18N".

I've created the centroids using the usual tool. I could then extracted the coordinates using the "Vector > Geometry Tools > Export/Add Geometry Columns", or saving the layer in CSV typing "GEOMETRY=AS_XY" in the "Layers" part of the "OGR creation options".

Nevertheless, both methods output Cartesian coordinates, whereas I need Lat/long coordinates.

merged by underdark Apr 2 '18 at 12:12

This question was merged with How do I calculate the latitude and longitude of points using QGIS? because it is an exact duplicate of that question.