/* Total size of all the indexes on each table, descending by size */

SELECT

c.relname AS table,
pg_size_pretty(pg_indexes_size(c.oid)) AS index_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_indexes_size(c.oid) DESC;