/* Total size of all indexes in MB */

SELECT

pg_size_pretty(sum(c.relpages::bigint*8192)::bigint) 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='i';