What is the difference between どうかな and どうなんだろう?


My native Japanese friend said that both どうかな and どうなんだろう can be translated as
"I"m not sure". Do they actually mean the exact same thing? Or are there
subtle differences in their usage?




どうなんだろう is more explicit about the fact that the speaker is unsure and
wondering about something. どうかな can be used in broader situations.

どうかな tends to be used when the speaker knows the answer:

> A 「どうだった？ テストは合格だった？」  
>  B 「さあ、どうかな？」 (≒ "Hehe, guess what.")  
>  A 「もう、意地悪しないで教えなさいよ。」

And compare the two sentences:

> 1 「新しい服を買ったんだけど、どうかな？」  
>  2 「新しい服を買ったんだけど、どうなんだろう？」

Both どうかな and どうだろう basically translate to "what do you think?" here, but in
the former sentence the speaker is confident and expecting a positive
reaction, while in the latter sentence the speaker is unsure and asking for a
listener's opinion.




どうなんだろう is more explicit about the fact that the speaker is unsure and
wondering about something. どうかな can be used in broader situations.

どうかな tends to be used when the speaker knows the answer:

> A 「どうだった？ テストは合格だった？」  
>  B 「さあ、どうかな？」 (≒ "Hehe, guess what.")  
>  A 「もう、意地悪しないで教えなさいよ。」

And compare the two sentences:

> 1 「新しい服を買ったんだけど、どうかな？」  
>  2 「新しい服を買ったんだけど、どうなんだろう？」

Both どうかな and どうだろう basically translate to "what do you think?" here, but in
the former sentence the speaker is confident and expecting a positive
reaction, while in the latter sentence the speaker is unsure and asking for a
listener's opinion.

