PostgreSQL 9.5.14 Documentation /Chapter 28 / 28.1. Determining Disk Usage

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PostgreSQL 9.5.14 Documentation / Chapter 28. Monitoring Disk Usage / 28.1.
Determining Disk Usage
(Applies for other Versions, too.)

I'm wondering if the two statements given showing the index space size as
described.
I've the impression they show the space size of the tables.

Regards --Michael

Extract of the manual:

You can easily display index sizes, too:
SELECT c2.relname, c2.relpages
FROM pg_class c, pg_class c2, pg_index i
WHERE c.relname = 'customer' AND
c.oid = i.indrelid AND
c2.oid = i.indexrelid
ORDER BY c2.relname;

relname | relpages
----------------------+----------
customer_id_indexdex | 26

It is easy to find your largest tables and indexes using this information:
SELECT relname, relpages
FROM pg_class
ORDER BY relpages DESC;

relname | relpages
----------------------+----------
bigtable | 3290