Easier calculation of a surface using QGIS

I'm looking for an easier way to calculate the surface on QGIS:

My project CRS is in Lambert93.

Currently, when I'm calculating a surface using QGIS, when the surface seems wrong, I always have to:

• "Save as..." my current layer under a new CRS (Lambert93 in my case, (see Capture 1).


• Then the new layer appears, and the $area calculation seems correct. (Capture 2)

My question is: this process doesn't seems very efficient as it creates new files on my computer; is there any other way to do this? (ie. without Save as... new layer, neither creating new files, ...)

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Capture 1 : Save as the layer under a new CRS (Lambert93)

Capture 2 : my $area is now correct !