If you are just following orders, please ask the person issuing them how much usable space each filesystem needs for present and future requirements.
You want to make sure that you're not creating nearly-full filesystems from the start!
This approach to filesystem allocation is not scalable, so I strongly suggest that it be redesigned with a more modern filesystem or volume-manager like ZFS (or even btrFS). Those would allow the presentation of a pool of storage with multiple directories that can have individual attributes and quotas. But if you're stuck with the existing solution, you shouldn't be the one dictating the sizes of each volume.
If you must, though, test an XFS filesystem creation and see how much usable space results. In general, formatted XFS volumes have less overhead than like-sized ext3/4 volumes. So you'll have more usable space than you expect.