$ flatpak list --columns=size,name | grep MB| grep -Po '\d+\.\d+'| paste -sd+ | bc
  7025.2

  $ flatpak list --columns=size,name | wc -l
  54

  $ df -h /
  Filesystem      Size  Used Avail Use% Mounted on
  /dev/sda3       232G   15G  214G   7% /