Postgres: check disk space taken by materialized view?

I know how to check the size of indexes and tables in Postgres (I’m using version 9.4):

SELECT
   relname AS objectname,
   relkind AS objecttype,
   reltuples AS "#entries", pg_size_pretty(relpages::bigint*8*1024) AS size
   FROM pg_class
   WHERE relpages >= 8
   ORDER BY relpages DESC;

But this doesn’t show materialized views. How can I check how much disk space they are taking up?