convert MB to GB in powershell code example

Example 1: powershell bytes to mb

$window.FindName("TargetSizeKB").Text = "500"
$sizeKB = $window.FindName("TargetSizeKB").Text -as [int]
# Umrechnung in MB
$sizeBytes = $sizeKB * 1000

Example 2: powershell convert text 20MB to bytes

$str = '3GB'

$int64 = [int64]$str.Replace('GB','') * 1GB