Overall Folder Size is a groovy app that does what it advertises.

To open files, it will first brings you to the directory using the default Windows File Explorer. What I like is that the program can also be used as a file browser. As with folders, this can be set to rank based on the entire drive or specific subfolders. Space used can also be sorted showing which files are the largest. These size rankings can be adjusted and narrowed down into very specific sub folders if needed. With default settings, this shows the top space users on the system. System space can be sorted by folders across the entire system. Best of all, it’s available in a portable version that doesn’t require installation. It looks similar to Windows File Explorer and anyone used to Windows should be able to figure out how to use it right away. The program features a simple yet effective graphical user interface.

Folder Size is a freeware program that aims to solve this by scanning a drive only when you request it.

Windows folder size tool