Deck size is different on desktop and mobile

I just wonder why is that deck size on ipad/iphone are different from desktop?

I have two decks and each one is almost 4 gb on anki desktop.But when I look up in storage in my ipad and iphone, anki takes up only 4.5gb storage.Why is that? Isn’t it supposed to be almost 8 gb ?

I synch everything perfectly and everything runs smoothly.It is only curiosity.

edited: 8 gb*

Possible reasons for a difference:

  • backups
  • after deleting material, space is not reclaimed immediately