Database size in specific metrics

Good day all

I am really hoping that someone can help me out here.

I have a server (as example) with 24 postgresql databases running
on it. Each database differs in size from a couple of kb to a couple of
Gb.

When using these different sizes to try and create charts which
will show the database growth, I am having some issues.

The reason for this is that all the values are stored / noted in
the spreadsheets with the specific metric such as kb, mb,etc... next to
it in order to differentiate between them.

In order to be able to create the chart, the values however
must only contain the numeric values with no metric values.

I am running the following commands to retrieve the database
sizes:

for i in `psql -t -c "select datname from
pg_catalog.pg_database d" | grep -v template0 | grep -v template1`; do
echo $i;psql -d $i -t -c "SELECT pg_size_pretty(pg_database_size('$i'))
As fulldbsize;"; done

My question:

Does anybody know of a method to retrieve the sizes,
however , by specifying in which metric it should be displayed? (i.e.
1Gb will be returned as 1024Mb).

I would really appreciate it if someone can assist with this.

Regards
Machiel