You can always look up the mass that the FAC's have calculated with aerodynamic data via the AIDS pages in the MCDU.
Look for "Alpha Label" and enter GWFK (kg) or GWFL (lbs) and compare it to GW (ECAM, FMGS or also with the GW Alpha Label)
However, I don't know how accurate this is. I've seen GWFK being 2 tons more than GW.