This Powershell script can be used to calculate package sizes for multiple packages in ConfigMgr.  You can select which package/s you want to calculate the sizes for in a window, or optionally select a console folder and calculate the total size of all packages in that folder.

The total size of all selected packages will be reported, and using the -Verbose switch, individual package sizes are reported too.

It will work for almost anything in the Software Library, including:

- Applications

- Standard Packages

- Driver Packages

- Software Update Packages

- OS Image Packages

- Boot Image Packages

Full description on my blog: