Missing 4GB of Storage

[Salval]

I've wiped everything in TWRP but it only shows 12,206MBs of space. How can I get the rest of the 16GB back? Thank you.

 

[demkantor]

I've wiped everything in TWRP but it only shows 12,206MBs of space. How can I get the rest of the 16GB back? Thank you.

I don't have my tablet in front of me but my assumption is this is normal
You may have 16GB in advertised internal memory but this is never the case as a portion will contain firmware such as bootloader radio and the OS
Good thing you can add an sd card!