I asked a previous question about clarification of storage on an iPad. I included detail which didnt seem to be transmitted.

Storage available 17.6GB available >

Storage: (This I find confusing. Unless Total Storage 0 bytes means that I have used the free 5GB. The Available Storage of 1.7GB is what I have used not what I have left to use.)

Total Storage 0 bytes

Available 1.7GB

Manage Storage >

Photos

iCloud Photo Library 25.1MB

Backups 2.2GB

Lee's iPad 1.7GB

Margaret's iPad 531.3MB

Note that the figure of 2.2GB for Backups is the same as the sum total of the Apps for Margaret and Lee's iPad and that although the figure for Notes is not shown it is hidden in the sum of the Apps since the actual figures for the Apps do not quite equal the figure for the Backups. The actual figures sum to 1.450GB leaving 250MB for"the others" which includes my Notes.

The initial free 5GB of storage for the iCloud and with the purchased 20GB make up the 25GB of the iCloud Photo Library.

This leaves the sum for the storage as:

Mail 7.2GB plus

Available 17.7GB of the 20GB purchased giving the total of 24.9GB.

So my photos although they seem to be many, actually 1,584 photos and 8 videos use up 1.3GB of store which is approx 816KB per photo.