The amount of available, practical, usable storage is based not only on how much iOS/iPadOS takes up but on the actual size that 1.0 GB is equivalent to, which for Apple 1.0 GB ≈1.075 GBs
Also, iOS/iPadOS devices need to maintain a minimum constant of between 2-4 GBs to ensure nominal, expected performance and function of iOS/iPadOS.
Also, my “current” installation of iPadOS 13.2.3 takes up approx. 5.5 GBs of my iPad's internal storage space.
A 32 GBs storage iPad starts out with approx 30 GBs after internal drive formatting. Minus 5.5 GBs for iOS/iPadOS, leaves 24.5 GBs.Minus 2-4 GBs for iOS iPadOS system reserve equals approx. between 20.5- 22.5 GBs of practical, usable data storage space.
If you need to free up free data storage space on an iPad/iDevice, you need to start by backing up your iPad to either Apple's iCloud or by connecting your iDevice to a computer running the latest iTunes and/or some other offsite, “cloud” data storage/backup services, like Google Drive/Photos, DropBox, BOX, Amazon Cloud Drive, Flickr ( for photos/images ), etc.
Then, delete any installed apps that you no longer use or use infrequently enough that they aren't missed (you can always reinstalled any purchased or free apps at some time later, as you need them).
A disclaimer to the immediate advice above, if you own a 8 or 9-year old iPad, you SHOULD ONLY delete apps that you have ever seldom used or no longer use as there is NO WAY now, in 2020, to retrieve these old apps from the iOS App Store, any longer.
( Third party iOS app developers have permanently removed all of their older, legacy apps from Apple's iOS App Store servers forever!
There are NO more older, common and popular third party apps for old 8 and 9-year old iOS devices, any longer! )
Then, thin out/delete any music/videos/movies/TV shows/podcasts/screen recordings/images/eBooks/
eMagazine/iBooks/audio books/Documents/PDFs, etc.
If you use a POP email account on your iPad, delete/thin out any old saved emails that maybe saved to your iPad.
To permanently delete photos/images off of your iDevice go into the Photos app and find the Recently Deleted folder/album and permanently delete any photos/images stored in that folder/album.
Also, you can check to see what other stuff is eating up all your valuable data storage space by going into the Settings App,,General Settings Panel, in the right hand column, tap Storage & iCloud usage panel ( in iOS 11, it’s iPad Storage ), in the top Storage Panel, tap the Manage Storage panel, wait for a list of apps to generate that will tell you how much space each app is taking up on your iDevice.
Then, do a hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.
iOS devices and iOS/iPadOS need to maintain, at the very least, a minimum of between 2-4 GBs of free data storage space, AT ALL TIMES, to insure normal/nominal functionalities/operation and general overall performance of any iOS device running iOS/iPadOS.
If none if this has worked for you so far, then tap and read/follow the directions in the links below.
How to back up your iPhone, iPad, and iPod touch - Apple Support
Erase all content and settings from iPad - Apple Support
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
Best of Luck to You!