Sometimes, it is quite difficult to know exactly the amount of space stored inside your current system.
Now you can use Cloudsfer analyzer tool for free and you will be able to know exactly the expected size that is required for your data migration project (e.g. Dropbox to amazon s3).
It is so easy, just choose your own folders in the source system and scan it. You will get a detailed report with folders count, data volume, file type, and more…