The following Get-DisplayFileSize function takes any byte value and returns a nicely formatted size, using units like “MB”, “GB”, or “PB”:

function Get-DisplayFileSize 
    $newNumber = $Number
    $unit = ',KB,MB,GB,TB,PB,EB,ZB' -split ','
    $i = $null
    while ($newNumber -ge 1KB -and $i -lt $unit.Length)
        $newNumber /= 1KB
    if ($i -eq $null) { return $number }
    $displayText = "'{0:N2} {1}'" -f $newNumber, $unit[$i]
    $Number = $Number | Add-Member -MemberType ScriptMethod -Name ToString -Value ([Scriptblock]::Create($displayText)) -Force -PassThru
    return $Number

Here are some examples:

PS> Get-DisplayFileSize -Number 800
PS> Get-DisplayFileSize -Number 678678674345
632,07 GB
PS> Get-DisplayFileSize -Number 6.23GB
6,23 GB

What’s really interesting is that the function does not return strings. It returns the original numbers and just overrides its ToString() method. You can continue to sort, calculate, and compare:

PS> $n = 1245646233213
PS> $formatted = Get-DisplayFileSize -Number $n
PS> $formatted
1,13 TB
PS> $formatted -eq $n
PS> $formatted * 2
PS> Get-DisplayFileSize ($formatted * 2)
2,27 TB

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