Invoke-SumSize.ps1

    function Invoke-SumSize {
        # I don't wanna type out the full name every time... Add an alias for me.
        [alias("iss")]
        param (
            [parameter(
                ValueFromPipeline
            )]
            [Alias('Length')]
            [ValidateNotNullorEmpty()]
            # Removed type enforcement on the input object because there are several possible types they send in on
            # and if their input object doesn't cast to double and propertyname and propertyname alias also doesn't cast
            # to double, then we'd just rather keep going without big errors.
            $InputObject
        )

        begin {
            [double]$Total = 0
        }

        process {
            # Because people may pass in a single object containing several values that you actually want to operate on
            foreach ($Item in $InputObject) {
                if ($Item -as [double]) {
                    $Total += $Item
                }
                # Use PSObject.Properties method of getting Length so that we avoid cases where powershell auto-returns
                # a number on an array of X length and also check that we are not dealing with a string of X length
                elseif ($Item.PSObject.Properties['Length'].Value -as [double] -and -not ($Item -is "String")) {
                    $Total += $Item.Length
                }
                else {
                    # If we can't cast it, then let the non-terminating error float on up
                    [double]$Item
                }
            }
        }

        end {
            switch -Regex ([math]::truncate([math]::log([double]$Total, 1024))) {
                '^0' { "$Total Bytes" ; Break }
                '^1' { "{0:n2} KB" -f ($Total / 1KB) ; Break }
                '^2' { "{0:n2} MB" -f ($Total / 1MB) ; Break }
                '^3' { "{0:n2} GB" -f ($Total / 1GB) ; Break }
                '^4' { "{0:n2} TB" -f ($Total / 1TB) ; Break }
                '^5' { "{0:n2} PB" -f ($Total / 1PB) ; Break }
                # When we fail to have any matches, 0 Bytes is more clear than 0.00 PB (since <5GB would be 0.00 PB still)
                Default { "0 Bytes" }
            }
        }
    }