You may notice that the used space shown for a Linux ext partition in Macruim Reflect is larger than shown in Linux.
The above is after a fresh install of Linux Mint on a dual booting Windows 10 and Linux Mint system.
Notice that the reported file system size for the '/home' partition is 980.43 GB and the used space is 15.55 GB
Viewing the same file system in Linux can yield different and incorrect results. The following is the output from running 'sudo df -h'
Notice that the same partition is shown as having a total size of 965 GB with a used space of only 110 MB.
Reflect is showing the used space is approx 15 GB larger and and the file system size is approx 15 G larger, on a fresh install of Linux!
Why the difference?
Macrium Reflect uses the ext super_block structure to report the total and used space of the file system. This should always be correct and includes 'reserved' blocks for root which is usually up to 5% of the file system.
The following is the output from running 'sudo cfdisk'. 
The output from running 'cfdisk' matches the Reflect total file system size exactly and includes reserved data blocks.
The difference between 980.4 GB and 965 GB is the same as the difference in the reported used space by Macrium Reflect.
Running 'sudo gparted' should agree with the numbers reported by Reflect:
These numbers agree with those shown by Macrium Reflect,
See also: Browsing Linux Ext File System Images