explaining the pg_total_relation_size/pg_relation_size results

I have the follwing in a view to glance at the size of my relations:

pg_size_pretty(pg_relation_size(c.oid::regclass)) AS size,
pg_total_relation_size(c.oid::regclass) AS bytes

This view sorts by pg_relation_size(c.oid::regclass) descending.

The question is: the byte values are often higher for relations with a
lower size indicated by size. As I sit here, I see an 11GB table
of 23821893632 bytes and a 12GB table of 14545387520 bytes, and
lastly/weirdly, a 3194MB table of 19924844544 bytes.

Can someone give me the quck explainer here of what I am looking at? I tend
to trust the size more than the bytes but I want to understand both better.

Thanks.

--
Wells Oliver
wells(dot)oliver(at)gmail(dot)com <wellsoliver(at)gmail(dot)com>