How many encounters per day? (D&D 5e)

The DMG says 6-8 on page 84:

Assuming typical adventuring conditions and average luck, most adventuring parties can handle about six to eight medium or hard encounters in a day. If the adventure has more easy encounters, the adventurers can get through more. If it has more deadly encounters, they can handle fewer.

So that's settled, see you in the next post. ;)

Just kidding.

Regardless of being more or less explicit, this generates endless discussion online: are 6-8 encounters needed? Could you replace them by fewer, tougher encounters as the DMG suggests? Or this is just a matter of taste and it can vary from table to table? Are these COMBAT encounters or ANY encounters?

IMO, the game is build with the expectation of 6-8 combat encounters per day, and it is not easy to break away from this - and it is not the same if you just throw harder encounters at your party.

Take a look at the barbarian. He or she progresses from 2 to 6 rages per day, only getting unlimited rage at level 20. This means that, obviously, he is expected to have more than 2 encounters per day, or the rages would be effectively unlimited form level 1. It ALSO means that you will frequently have more than 6 encounters per day for the same reason (otherwise, we could just say "unlimited" earlier).

The barbarian is the best example but not the only one. Many class features can be used a number of times equal to your main ability modifier (usually ranging from +3 to +5) and, recently, equal to your proficiency bonus (from +2 to +6) per day. Bardic inspiration is another example.

Notice that HP follows a different reasoning, since it is more granular (i.e., you can lose 30 HP in three different combats and just heal it all at once).

Unlike rage, you could say that a harder encounter would force PCs to "spam" their abilities, but that's not always easy to do, since most combats will not last for more than three or four rounds anyway. Some features have a duration that indicates they'll last for the entire combat (e.g., 1 minute), so there is no point in using it again. 

Abilities that can be "spammed" or used more often (e.g., superiority dice) are usually based on short rests.

Spellcasting is somewhat similar, but not exactly; you can cast your "best" spells from 1 to 3 times a day. These spells are often more powerful than most features, however, which is why they are meant to be used less often. If you have only two or three encounters per day, wizards - an already powerful class -  might completely outshine other PCs (e.g., the barbarian). In addition, the wizard recovers some spell slots on short rests.

Non-combat encounters? Well... most class features I've mentioned above are about combat. Sure, maybe a trap or obstacle can use a spell slot or two, but hardly a rage, superiority dice or divine smite. Social encounters? That is even harder; there are few expendable features to use here.

There are also "per encounter" features, but they are relatively rare (they usually have something to do with roiling initiative, which means combat).

Can you use a different number? 

Yes, of course. But it is not easy to balance. Twelve different encounters a day with few short rests would be though for wizards... but that's a lot of encounters, and I can hardly imagine even a professional soldier during war having that many.

Maybe sending wave after wave of weak enemies would be interesting; let combat drag on for a minute or more, let martials (and rogues) shine, etc. This might make sense if you dealing with a disorganized army or even invading a dungeon and making noise, so you can fit 6-8 encounters or even more without sounding absurd. If you send them all at once, a fireball will solve the issue faster.

In short, the game is built for dungeons full of monsters in separate rooms.

Is there an easy solution? Well, there are various solutions, but not necessarily easy. You could use HD to power your features, for example, and introduce a 5-min rest to recover some HD right after a fight. You could make it harder to rest in the wild, which would allow you to have dungeons full of encounters and wilderness with one or two per day at most. Or divide your session in expeditions instead of days.

But, ultimately, it depend on the type of the game you want to run, and using the same rules for hexcrawls and dungeoncrawls is not easy.