Is your iPad jailbroken? Simply jailbreaking or getting content for it adds files that arent calculated by iTunes. Also, the IOS and system files take up space, along with system partitions space. Even if there is nothing on your iPad, there will still be space taken up.
16gb-1.6gb(Partition data (Ratio deducted from a 64gb version, giving 58.7gb))-8.1gb=6.3gb-0.92gb=5.38gb
what should be in
Other:
- Emails
- Attachments
- Contacts
- Calendars
- Bookmarks
- File downloads from the internet
- In-app downloads
- Podcasts from independant apps
- Videos imported into 3rd party media players
- Cydia Files, tweaks and addons
Just to name some of them.