“So I had switched iTunes to download 720p movies instead of 1080p. (You can do this in iTunes > Preferences > Store),” McElhearn writes. “But I saw today that the iTunes Store has the extended versions of The Lord of the Rings trilogy in HD for only $30. I don’t have them on disc; I used to have the Blu-Rays, but gave them to my son. I wanted to buy them, and was curious to see how much difference there is between the two different qualities.”
McElhearn writes, “A difference of 1.4 GB; or about 5% more to get the 1080p versions instead of the 720p versions. And that affects not only your download size, but also the amount of storage you need.”
Why the difference is so slight in the full article here.