WhatSize allows you to quickly measure the size in bytes of a given folder and all subfolders and files within it. You would be surprised at how many useless files might be laying around on your hard disks. The files and folders are automatically sorted by size, with the biggest sizes first. WhatSize helps find out what files are taking up all of that space. Then it makes it really easy to remove or move those files. You'd be surprised how many useless files are lying around on your Mac's hard disk.

While the app is measuring a folder the user can browse the files within that folder and immediately see the size in bytes. Hidden files, cache files, directories will all show up with their corresponding size. This application is similar to the ancient NeXTSTEP, DarkForest.

Once the measuring of a folder has ended the user can also view the information by filtering for particular file sizes or types. The user can also move unwanted files and folder in the corresponding Trash bin similar to the Finder's Delete button.