explaining the pg_total_relation_size/pg_relation_size results

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.