TLDR: I keep running out of space before bacula cycles the volumes and
re-uses previous ones. How do I properly calculate volumes and how long
I should keep them?

Background:

I have numerous jobs (too many to include here), but let's say I know
that a full backup for a given job, X is 50GB. Incrementals are (on
average) around 500MB / day. Therefore, in my mind, I should alot 57GB
for this backup for every two weeks. I have set the retention period for
the job and the volume for two weeks. I have done this formula all my
jobs, and configured the Maximum volume bytes and Maximum volumes to
house all this (it so happens that 2 weeks of data for all jobs should
be a total of 2.2 TB. I am using an external HD that is 5TB.

Somehow, I am still running out of appendable volumes. To bandaid the
issue, I just raise the Max volumes amount and let backups continue on
because "I'll come back to fix this later." Now, I have raised them to
185 and I am nearly out of space on the 5TB drive - and I am (once
again) out of appendable volumes. So, it's really got to be fixed now.

Is this the correct calculation method for how much space I should be
consuming? What am I missing?

## File Pool definition
Pool {
  Name = File
  Pool Type = Backup
  Recycle = yes                       # Bacula can automatically recycle
Volumes
  AutoPrune = yes                     # Prune expired volumes
  Volume Retention = 2 weeks          # same as everything else.
  Maximum Volume Bytes = 30G          # Limit Volume size to something
reasonable
  Maximum Volumes = 185               # Limit number of Volumes in Pool
  Label Format = "Vol-"               # Auto label
  Action On Purge = Truncate
}