我不太確定。

I can't say for sure.

I don't know for certain.

Source: Tatoeba

Sentence Composition

1 我 wǒ
  1. I
  2. me
  3. my
2 不 bù
  1. no; not so
  2. (bound form) not; un-
=3 太 tài
  1. highest
  2. greatest
  3. too (much)
  4. very
  5. extremely
=3 太 tā
  1. (Korean Classical Chinese) soybean
  2. (obsolete on its own in Standard Chinese) only used in 太末
  3. only used in 太末
  4. soybean
4 確定 quèdìng
  1. definite
  2. certain
  3. fixed
  4. to fix (on sth)
  5. to determine
  6. to be sure
  7. to ensure
  8. to make certain
  9. to ascertain
  10. to clinch
  11. to recognize
  12. to confirm
  13. OK (on computer dialog box)