I am discussing via email about a file, and I want to ask "What is the size of the file?"
Here is my try: サイズは何ですか？
I realize it sounds weird though, and サイズはどのぐらいですか？ might sound better but I am afraid that the ぐらい will imply I want an approximate size, which is not true: I want the exact size.
A natural way of asking that would be:
「ファイルのサイズを[教]{おし}えてください。」
If it is for business, one could say:
「ファイルのサイズをお教えいただけますか。」
The problem with 「サイズは[何]{なん}ですか？」 is that while it is a perfectly grammatical sentence, it sounds like it was "translated" from anothet language, which it was. When I read that part, it reminded me of the sentence 「[名前]{なまえ}は何ですか。」 which is also often said by Japanese-learners.
