/* Size of the tables (excluding indexes), descending by size */

SELECT

c.relname AS name,
pg_size_pretty(pg_table_size(c.oid)) AS size

FROM

pg_class c

LEFT JOIN

pg_namespace n ON
  (n.oid = c.relnamespace)

WHERE

n.nspname NOT IN ('pg_catalog', 'information_schema') AND
  n.nspname !~ '^pg_toast' AND c.relkind='r'

ORDER BY

pg_table_size(c.oid) DESC;