[DNSB]

If you have, for example, a PDF, azw3, ePub and txt file, the size shown is the largest file.

If you have a 250MB file and and 247MB file, the file size will be shown as 250MB.

For the file size, when I look in calibre, there is a file shown as 367MB, when I open the folder the largest file shows as 375,772KB. Dividing 375,772 by 1024 gives me 366.96MB so round up to 367MB while Windows file properties will round down to 366MB.

In your example, the 547 is likely the first three characters of the file size in bytes. 547,000,000 bytes gives me 521.65MB (divided twice by 1024) while 547,999,999 gives me 522.61MB.