I think your calculation is correct, i still dont understand why my party (party of level 4, Rogue, Hunter, Fighter and Barbarian) went through 21 orcs and a orc war chief in one encounter.
We're playing a non magic campagne, something happened 500 years ago and were trying to find magic back in the world.
But shouldn't we NOT been able to kille 21 orcs (CR 0.5) and a orc war chief (CR 4), even if there were first 3 orcs, then 4 orcs, then 5 orcs, then 4 orcs and then 4 orcs with a warchief.
If I look at the whole encounter, we had 5 small encounters, with the CR of 1.5, 2, 2.5, 2 and 6.
Which make total exp according to the book,
3 orcs = 3x 100 xp x2(multiplier for 3-6 mobs) = 600 xp
4 orcs = 4x 100 xp x2(multiplier for 3-6 mobs) = 800 xp
5 orcs = 5x 100 xp x2(multiplier for 3-6 mobs) = 1000 xp
4 orcs = 4x 100 xp x2(multiplier for 3-6 mobs) = 800 xp
4 orcs + warchief = (4x 100 xp + 1100xp) x2(multiplier for 3-6 mobs) = 3200xp
600+800+1000+800+3200xp makes a total of 6400xp.
IF u look at a deadly encounter for 4 level 4 chars, thats 4x500 xp, so how can we survive a 3 times as deadly encounter.
After that we killed a group of 19 orcs and warchief and oroc.
After that we killed a group of 10 Ogres.
before we found the first group orcs, we just dinged level 4, and now were almost level 6. Is my math completely wrong?
If they didn't all rush you at once, you faced five encounters, not one. Maybe you didn't get much (any?) rest in between, which would make it a bit more difficult, but they're still not really a single encounter. In the first four encounters, only one even clears the threshold for "medium" difficulty, the rest are "easy". And the DMG says to not even count monsters well below the average CR in the encounter when modifying xp for big mobs, so I don't think the regular orcs should count for doubling the xp of the final warchief encounter. Which would leave it at just barely clearing the "hard" hurdle.
So if you'd faced 21 orcs & their chief all at once, yes, there might be a good chance of TPK. But breaking it up into chunks makes a BIG difference.