Question HDD showing less space then what is calculated - appreciate any help

[tmuscat124]

I recently noticed that when I sum up the folders sizes in my HDD partitions, they do not add up to the total storage capacity for each partition that shows in Windows 11. I have the primary SSD C: (231GB) and another HDD which has 3 partitions, D: (62GB), E: (30GB), and F: (57GB).

I am aware there are some MB for the recovery partition in Disk 1 however, as you can see below, there are discrepancies between what I calculated from the folders' sizes to what is actually showing as free on the PC.

I am at a loss to why there is such a discrepancy in all partitions. Appreciate any help you might provide.

Thanks

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Drive name	Total Size	Calculated used space	Supposed free space (Size - calculated)	Actual free space showing	Discrepancy
C:	231GB	114GB	117GB	87.3GB	~ 29.7GB
D:	62GB	44.9GB	17.1GB	6.62GB	~ 10.48GB
E:	29.9GB	13.1GB	16.8GB	6.79GB	~ 10.01GB
F:	56.9GB	19.3GB	37.6GB	31.5GB	~ 6.1GB

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[USAFRet]

Many reasons
Hidden files/folders
Pagefile
Hibernation

Sector size vs actual data.

For instance, in your C drive on the left.
Size on disk: 114GB (122, 381, blah blah) The 8GB difference there is the difference between actual data, and sectors.
A file of 1k in a 4k sector consumes 4k. The 3k is that difference.