Comment by mb4nck

For the record, on Debian unstable:

  root@pg1:~# LANG=C apt install postgresql-12 
  Reading package lists... Done
  [...]
  0 upgraded, 32 newly installed, 0 to remove and 0 not upgraded.
  Need to get 59.7 MB of archives.
  After this operation, 240 MB of additional disk space will be used.
  Do you want to continue? [Y/n] ^C
  root@pg1:~# LANG=C apt install postgresql-12 postgresql-12-postgis-3
  Reading package lists... Done
  [...]
  0 upgraded, 105 newly installed, 0 to remove and 0 not upgraded.
  Need to get 104 MB of archives.
  After this operation, 418 MB of additional disk space will be used.
  Do you want to continue? [Y/n]

I think the addition of LLVM for JIT execution of plans added a lot to the Postgres install baseline (at least in distribution packages, you can compile a much leaner postgres yourself).