Being Tricky
The short answer
A "Google Photos storage full" warning really means your Google Account storage is full: 15 GB shared by Gmail, Drive and Photos.
At a glance
About 25 minutes · Advanced · For Google
Key point 1 of 5
Every Google Account comes with up to 15 GB of storage, shared across Gmail, Google Drive and Google Photos.
Key point 2 of 5
Before deleting anything you might want later, save a copy to your computer or an external drive.
Key point 3 of 5
Google Photos has a built-in cleanup tool that groups items you may not want, such as large photos and videos, screenshots and blurry photos.
Key point 4 of 5
Items you delete sit in the trash for 30 days before Google removes them permanently.
Key point 5 of 5
If you back up in Original quality, you can shrink what's already in your library.
Quick tip
Deleting a photo saved before June 1, 2021 in Storage saver doesn't free any storage, because it never counted.
Watch out
Deleting a photo in Google Photos also removes it from your other phones and tablets with backup turned on, and from albums and shared albums.
You might ask
Why is my Google Photos storage full when I don't have many photos? The 15 GB is shared with Gmail and Google Drive.
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Being Tricky