Both are very large estimations:
Do we have any idea how comparable are both events in terms of death count? Just to be clear, I'm not trying to justify the bombings or anything; just making comparisons for research.
Both of these have very large uncertainty bars around them, as one would expect for massive wartime events with poor record-keeping. They are different sorts of events, though. I would note that "genocide Olympics" ("who killed more, X or Y?") is considered a form of /r/badhistory — it does not enlighten these events very much.