How to estimate the number of rows and size of tables in Postgres DB?

How to estimate the number of rows and size of tables in Postgres DB?

select
    nspname as schema,
    relname as tablename, 
    to_char(reltuples, '999,999,999,999') as rowcounts,
    round(pg_relation_size(c.oid)/1024/1024/1024) AS tablesize_gb
  from pg_class c JOIN pg_catalog.pg_namespace n
   ON n.oid = c.relnamespace where relkind='r' and nspname = 'public' 
   order by nspname, reltuples desc;