Well im not to sure if its differant for each type of egg but my riolu egg hatched in about 6,600 steps.
Hope this helps.
Bulbapedia says it takes 5355 steps to hatch
improved:
i breeded infernape with ditto and my chimchar egg hatched at exactly 5323 steps
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About 5000
It takes 5,376 steps for a chimchar egg. And If You have A Pokemon with Both Magma Armor And Or Flame body, 5,376 Steps Become 2,688. If You want Email Me At: Matthewbny20008@AOL.com or go to Pokemon.marilland.com for more hatching egg steps.
It takes 7,680 Steps to hatch a Cranidos. And it hatches faster when you have a Pokemon with the ability Flame Body
you can't hatch a pikachu egg on diamond, it hatches in to a pichu.
I just recently breeded my Floatzel with my Piplup and made a Piplup egg and restarted my counting app on my PokeTech and it turns out that it hatches within 5355 steps. Hope This Helps!!