Kessler is about 6'2" on the fight camp or any other picutres i see of him he does not look much bigger so i would say about 185-190. He has fought at LHW before and looked sturdy there. Its not odd to think he weighs about 10 more pounds than that in between fights.
Felix sturm says he walks around 190lbs and he is only 5ft 11 middle weight of course. Mikkel id imagine walks around close to 200lbs.
I'd guess 190ish, he has a pretty solid build but 200 seems too high since he looks like he keeps in good form between fights.