How to get the storage space of a table in the MariaDB MyRocks stoage engine

I'm trying to get the space that a MyRocks table takes on disk and I'm getting inconsistent results. I'm using the following request:

select table_name 'Table Name', (data_length+index_length)/power(2014,3) 'Table Size in GB' 
from information_schema.tables where table_schema="MyTableName";

Which returns a really small number for what I'm doing, to the point where I'm doubtful that it's reporting the actual size (0.4GB for 4 000 000 rows with a lot of text).

If I run the command du -h /var/lib/mysql/#rocksdb/, I'm getting a disk size of 2.4GB, which is more or less what I would expect. However, if I understand correctly, MyRocks compacts data as data is inserted, so it's possible that the disk space reported by the du command is unrepresentative of the actual table size.

So, is there a reliable method to get the size of a table? Am I already using the correct way to get the table size?