Why is there difference in size?

Am still trying to get the already installed (in dual boot) Trisquel 9 to boot. Notice that for sda6 it says 426.6G Linux filesystem, sda7 7.9G Linux swap. But when I look at it in Caja with the bootable USB (with Trisquel 9) it says 458 GB Volume. What is the explanation that there is a size difference between what it says in Caja that is on this laptop, and the size it gives for sda6 when looking at it in a terminal with sudo fdisk -l ? Is it normal that there is a size difference? Is this size difference the reason why it doesn't boot, though it is in the boot order? Is there a way to get the size what it says in Caja down to what it says for sda6? Or the only way would be to increase the size of sda6? Any help is appreciated!