Your 64 GB drive shows 57 GB, and one of those numbers is marketing

A 64 GB drive shows as 57.6 GB, a 1 TB drive as 931 GB, and a 500 GB drive as 465 GB. None of these is a fault, and the arithmetic is the same every time.

Gigabytes against gibibytes

Manufacturers count a gigabyte as 1,000,000,000 bytes. Windows counts a gibibyte, 1,073,741,824 bytes, and labels it GB. That is a difference of about 7 percent, and it compounds: a terabyte drive loses about 69 GB to the conversion alone.

Then formatting takes its share

The file system itself needs space for its tables. On NTFS that is the Master File Table and the journal, typically a small percentage. A 64 GB drive showing 57 GB after formatting is that plus the conversion, and it is normal.

When it is not normal

• A drive showing far less than expected, such as 32 GB on a 64 GB stick, usually has a hidden or unallocated partition. Disk Management shows it.
• A drive showing more than it can hold is the classic counterfeit: firmware reports a large size and writes wrap around, destroying earlier data silently.
• A drive that shrank after use may have remapped failing sectors, which is a warning.

# Every partition, including hidden ones
Get-Disk | Get-Partition | Select-Object DiskNumber, PartitionNumber, DriveLetter, Type,
  @{n='SizeGB';e={[math]::Round($_.Size/1GB,1)}}

Testing a suspicious drive

If a drive was cheap and the capacity looks too good, write a known amount of data and read it back. Tools designed for this fill the drive with verifiable patterns and check them, which is the only reliable way to catch a counterfeit before it eats your files.

Reclaiming a hidden partition

Disk Management can delete an unallocated or leftover partition and extend the main one. On a drive that used to be bootable, or shipped with a manufacturer's software partition, that is where the missing space is.