Looking at your screenshot, I noticed that on some places there is 'GiB' and on others 'GB'
Somewhere in the back of my head, I remember a teacher at the university that told us there is a small difference between to two.
One is calculated as followed:
1 GiB = 1024 MiB = 1024 * 1024 KiB = ...
And the other is calculated as followed:
1 GB = 1000 MB = 1000 * 1000 KB = ...
Starting from this
you can find some more information on this. So the meaning on 'Megabyte, Gigabyte,...' can differ somewhat. Following defenition can be used:
1 MB = 1 000 000 bytes
1 MB = 1000 * 1024 bytes
1 MB = 1024 * 1024 bytes
Maybe this can explain the differences in different applications...