Why the big difference in reported file size?

[MrMister111]

Just had a look and my photo library taking up 678Gb in Finder, but on manage storage it shows 852Gb, that's quite a large difference!

Which is correct and why the massive difference? screenshot shows the manage storage app on the above and the finder on below?

 

[BLUEDOG314]

My guess is pictures not in your Photos library account for the difference. My Photos library is 32GB in size, but about this Mac reports photos are 44GB. I do have a good amount of stray photos not in my library because I don't want them there, and about this Mac also probably finds anything with certain extensions and totals it up. This could even mean cached images from browsers also count in that total.

 

[DeltaMac]

Storage would be the space those files need. If you use iCloud, and have your iCloud settings to allow less-often accessed files to automatically upload (clearing space on your drive), your system continues to report that space, even though that picture, or likely many of your pictures don't actually exist on your system until the next time you use that picture, when it would be automatically downloaded to your system. The space needed is still reported, even though it is not actually used. It continues to be reserved for that picture.

 

[MrMister111]

My guess is pictures not in your Photos library account for the difference. My Photos library is 32GB in size, but about this Mac reports photos are 44GB. I do have a good amount of stray photos not in my library because I don't want them there, and about this Mac also probably finds anything with certain extensions and totals it up. This could even mean cached images from browsers also count in that total.

I don't have any other pictures anywhere else apart from in the Photo library though. I've just done a recent clean install of v10.14 and recovered form iCloud my photo library.

Storage would be the space those files need. If you use iCloud, and have your iCloud settings to allow less-often accessed files to automatically upload (clearing space on your drive), your system continues to report that space, even though that picture, or likely many of your pictures don't actually exist on your system until the next time you use that picture, when it would be automatically downloaded to your system. The space needed is still reported, even though it is not actually used. It continues to be reserved for that picture.

I use iCloud library but have the option enabled to keep all originals on my iMac