aramis erak
Legend
All I have to add are two random assumptions.
1. As I understand it, the 5e game puts levels 1-3 as the "scrub" levels, where players are just starting their adventuring careers and are struggling to master their new roles as adventurers. I also understand that the XP chart makes quick work of gaining those 3 levels.
The math works out to about 10-13 moderate single-opponent encounters per level, or about twice that for 3-8 opponent moderate encounters. so, 10-26 moderate encounters per level.
But, note that that presumes a balanced levels party.
For players who only get to 2-3 encounters per sessions, each level is 3 to 13 sessions. (This could be due to in-character talkiness, table talk, short sessions, excessive grid reliance, GM's throwing easy encounters in sequence rather than harder ones...) Now, with 2.5 hour sessions, I saw players hit level 2 in about 5 sessions. Several hit level 2 in 4 sessions. On the other hand, playing in an otherwise level 3 party, the last two new guys both hit level 2 in one session. The guy who made level 2 made level 3 in 3 more sessions. In other words, it catches up quickly. 12 sessions in, and my players are mostly hitting level 4. And leveling out of Encounters into Casual Play at the store...