How is the size of an LVM volume calculated?

Today I'm configuring kickstart, and when I tried to set the LVM sizes, Anacond protests that there is no free space to create LVM with VG size. Well I could figure out that --grow option can continue the installation w/out prompt to solve this problem, but I need to know how I can calculate the correct VG size to group my LVMs? I just could see something related in AIX system but I thing that is not about my question, and no that isn't a bug.

Error:
storage configuration failed: ('new lv is too large to fit in free space', 'vg00')

The wrong configuration:

The correct configuration:

When I used the --grow option in partition, the kickstart create a anaconda-ks.cfg with that configuration above, I just can't understand how the size=14079 is calculated. The original-ks.cfg have the option --grow ;)

Could someone give a idea about LVM math?

Thx