I needed to give a customer an estimate on how much space would be saved if old files were moved off of the server into cloud storage, such as Amazon S3. While there are lots of ways to do this, I broke out the old robocopy program and ran the following:

robocopy C: C:Robocopy /s /e /minage:1095 /L /V /NP /TEE /Log:C:oldfiles-1095d.txt

This tells robocopy not to copy any files during the operation. The purpose of changing the directory being copied too is to ensure robocopy doesn’t find duplicate files and inadvertently skip them. The minage option tells robocopy to ignore any files newer than 1095 days old. Just wait a couple of minutes, and walla!, instant size estimate of the data.