What's the recommended level before starting Nightmare (or Hell) difficulty?

In Diablo II, what's the recommended level before starting Nightmare (or Hell) difficulty?

Solution 1:

I'm not sure if theres a real concrete answer to this. Different classes, built with different skills, with different items, played by different people will all function differently. Some characters (Like a minion-necromancer) will be able to handle higher difficulties at lower levels then say a mage (especially in hell when everything has multiple elemental immunities).

Without the expansion, I generally tried to hit nightmare around 35-40 and hell 50-60.

With the expansion, I tried to hit nightmare around 45-55 and hell 65-75. You'll want to be level up even higher if your playing a hard-core character.

Hope this helps

Solution 2:

One way to gauge is by using the following fact: those little fallens in act1 are level 36 monsters in NM and level 67 in H.