Discrepancy with iPhone storage
When I go to Settings - General - iPhone Storage I receive the information that I have "21.2GB of 32GB used". Roughly, 10GB free.
But when I plug the iPhone to a PC it shows me I have around 2.8GB free. The same amount (or approximately) appears in some apps, like Jukebox and Battery Doctor.
How can this happen? How can I know exactly how much free space I have in my iPhone?
iPhone 7, iOS 11.3.1