Hopefully I am under-thinking this issue. I've been going through my Photos library, deleting duplicates and lame pictures. When I went to look at the total library size, I got a different calculation in the Photos app compared to Finder. Photos says the library size is 603GB and Finder says it is 665GB. What is taking the extra 60GB? Is there something I'm missing here? Thank you for your help!
I assume Photos is reporting the total size of all the pictures (and just the pictures). This is sort of confirmed by selecting all the photos in the library and then using Get Info: this shows the same size as selecting the library.
Finder is showing the actual size of the library file on disk. This file contains all the photos but also a lot of other "meta" information about the photos, albums, places, faces, etc. that allows Photos to manage and display the pictures.
The photo library file on disk is actually a directory and you can descend into the directory. Finder normally wont do this because it knows it is a special directory (you can right-click on it and pick 'Show Package Contents').
A better way to get more detailed info is to open the Terminal utility and use the command line:
cd ~/Pictures/GKJones\ Fam\ Library.photoslibrary
(or just type enough characters to be unique then hit the tab key to auto-complete)
Then use the
du utility (display usage) to get a summary for each folder. I'd probably use the "depth" option (-d flag) and set the depth to 1 (only summarize to 1 sub-directory deep ... otherwise you'll get a very long output). Use the -h flag to put the values in human-readable format (the default is to display the usage as the number of blocks occupied)
du -hd 1
This will give you a list of all the sub-folders with the usage of each folder.
If you hold both [cmd] + [opt] while clicking the Photos icon to launch the app it will offer to repair the library. This takes a some time to complete depending on the size of your photo library.