If you resize your volume and the size or available space doesn’t match what you expected, there may be several reasons why:
The size of the filesystem that
df reports may be slightly less than the total disk size because some amount of the disk is reserved for filesystem metadata.
The sum of used and available space are slightly less than the reported total size because a small amount of space is reserved for the root user (typically 5% by default), and
df does not report this space.
Different tools report size in different units, like gigabytes (1 GB = 1000 bytes) or gibibytes (1 GiB = 1024 bytes). For example,
df -h reports size in powers of 1024, like GiB, and
df -H reports sizes in powers of 1000, like GB. 500 GiB is approximately 536 GB.