Q: Why does deleting photos to gain more disk space not work?

Deleted photos are retained for a week by default. If you really want to get rid of them now, use the Empty Trash command inside Photos.

because something is incorrect but since you give us no information no one can do anything except make wild guesses - one wild guess is that you migrated from iPhoto so the photos must be deleted in Photos and in iPhoto since they have two independent libraries - if you did migrate adn if you are positive you are done with iPhoto then archive the iPhoto library and delete it and empty the trash

LN

when I delete photos from "Photos" and the "Recently Deleted" album?

If you still have a migrated Aperture Library or iPhoto Library, you need to delete the photos from both libraries, as Larry explained.

The original library and and the new Photos Library are sharing the same entries in the file table by hard links and the storage will not be released, unless the files are deleted from both libraries.

For background reading:

Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

https://sixcolors.com/post/2015/02/the-hard-link-between-photos-and-iphoto/

Deleted photos are retained for a week by default. If you really want to get rid of them now, use the Empty Trash command inside Photos.

Grant - just curious - where have you seen the "one week" default?  The Photos Help (https://help.apple.com/photos/mac/1.2/?lang=en#/pht3bfab2f96) is incredibly vague and just mentions

Deleted items remain in the Recently Deleted album for the number of days shown, and then are deleted permanently.

When I delete a photo from my photos Library, it will always show 29 days right after the deletion, so I thought that would be the default, like for an iCloud Photo Library.

If you have iCloud Photo Library turned on, you can restore photos and videos from iCloud for 30 days before they’re removed from iCloud and your Mac

Have you seen a definitive number for a non-iCloud Photo Library somewhere?

léonie-

I have no definitive information about what the exact period is, but wanted to tell the original Poster that the despite appearing to delete them, their photos would be automatically retained for a non-trivial amount of time, unless they used the "Empty trash" inside the Photo program, not just the one in Finder.

I was quoting hearsay of "a week" from another user's posting. I am sorry if that was misleading in any way.

Your explanations including the issues of converting from iPhoto to Photos is much more detailed and useful than my quick, sloppy stab at a solution.

The OP stated

Why do I not gain disk space when I delete photos from "Photos" and the "Recently Deleted" album?

so according to them they choose no to wait the 30 days or so but immediately deleted them form the recently deleted album - in that case there is no delay and the most likely issues is still having the photo in the original iPhoto or Aperture library that they migrated

Untill they post back with more details we can only make guesses

LN

LarryHN--

The point was that simply deleting them inside Photos does not suffice, unless they used the "Empty Trash" inside the Photo program, not just the one in Finder.

Yes, we need more information.

Thank you, Grant for the clarification. I just hoped, there was a support document I missed.