Get Database size

select datname, pg_size_pretty(pg_database_size(datname))
from pg_database
order by pg_database_size(datname) desc;

           datname           | pg_size_pretty
-----------------------------+----------------
 ci5_orig                    | 73 GB
 ci4_orig                    | 73 GB
 ci5                         | 73 GB
 ci2_orig                    | 73 GB
 ci3_orig                    | 72 GB