Miller’s 1956 “7 + or – 2″ was the short term memory heuristic used for a long time in lieu of anything better.
I think now depending on how it’s measured, the number of items that can be remembered varies. A range of “3 sometimes 4″ comes to mind for some reason but I’m not sure for what range.
Ah here. Yeah, 3-5 chunks. It’s not that you can’t do more but beyond that takes more effort / some tricks.
In short: memorizing four items and struggling with #5 is: