pg_column_size()

Hi,

I'm trying to find the size of individual rows in a database (or a subset of
them) so that we can tell users how much of a quota they are using on the
system (in practice this will actually be across a number of tables and I
will need to write a query to do this). I have come across pg_column_size()
which obviously does the size of columns. My question is do I need to use
pl/pgsql and write a function to sum the columns in the rows and then the
required rows - or is there something similar i.e. pg_row_size (which
doesn't exist!) which I have missed.

Thanks

Jake