File size is a measure of how much data a computer file contains or how much storage space it is allocated.
Typically, file size is expressed in units based on byte.
A large value is often expressed with a metric prefix (as in megabyte and gigabyte) or a binary prefix (as in mebibyte and gibibyte).
[2] Generally, a file system allocates space in blocks that are significantly larger than one byte.
The file system allocates a number of blocks that together provide enough space to hold the file data.