얼마나 -(으)ㄴ/는지 모르다 — You don't know how..., So..., Extremely, Beyond words

This expression is used to emphasize the degree of a situation or state, indicating that it is beyond words or to an extreme extent. It corresponds to "You can't imagine how..." or "I can't tell you how..." in English.

Details

1. When used with a verb, this expression must be used together with a degree adverb such as 열심히, 잘, 많이 or 못.

자야 씨가 얼마나 공부하는지 몰라요. ✕

(Here, without the adverb 열심히 the sentence means that the speaker does not know the amount of time that Jaya studied. Thus a degree adverb is necessary.)

아키라 씨는 얼마나 많이 먹는지 몰라요. ✓

2. However, it is unnecessary to use a degree adverb when expressing the speaker's feelings or attitude toward something, such as with the expressions 짜증이 나다, 화가 나다 and 감동하다.

길이 막혀서 얼마나 짜증이 나는지 몰라요.

You can’t imagine how upset I was because of the traffic jam.

그 영화를 보고 얼마나 감동했는지 몰라요.

I can’t tell you how much I was touched after seeing that movie.

3. When used to refer to past situations or states of affairs, the form ‘-았/었는지 몰라요’ is used. Note that the ending verb 모르다 is usually used in the present tense.

어제는 바람이 많이 불어서 얼마나 추웠는지 몰랐어요. ✕

가: 도쿄 여행은 어땠어요? 재미있었어요? 나: 네, 그렇지만 도쿄의 물가가 얼마나 비싼지 몰라요. 물가가 비싸니까 쇼핑을 마음대로 못 해서 아쉬워요.

A: How was your trip to Tokyo? Was it interesting? B: Yes, but I can't tell you how expensive things were there. The prices were so high that unfortunately I couldn't shop like I had wanted to.