Showing low internal storage in Sony Xperia T2 Ultra when connected to PC

[Yash_pen]

I am proud owner of Sony Xperia t2 ultra and I am not using any SD card but I am facing a problem that it shows lesser internal space when connected to computer but in real it has more space left. My phone has around 2.5GB internal space left when I check from phone but if I connect to computer then it shows only 1.8 GB space available.

Now I can't copy big files in it when no space is left, where is my rest of the space which is shown in phone but not in computer ?