How to determine how many GB my iphone is?

My capacity is 13.3 and 9.3 is available, what GB is it?

It's a 16GB model. About 13GB is left for the user (capacity) after iOS & essential files & you have 9.3GB left of that 13GB you could use & 16GB total.

16gb. The operating system typically takes up 2.4-2.8 on it's own so it's 16gb total. No, you were never going to have access to the whole 16, nobody does. It's a marketing lie that they all get away with. Best luck.