To type the hiragana, you're probably using an IME like Anthy or Mozc. This IME should also allow you to convert the hiragana you typed into kanji. In Anthy and Mozc you do this with the SPACE key. To find out how to do it with the IME your using, you might need to consult the IME's documentation.
In most cases, the IME should offer you multiple kanji that fit your hiragana input to choose from. As I explained above, one kanji can have multiple readings, and multiple kanji can have the same reading. So, for example, if you type 「こう」, the IME has to "guess" whether you mean the kanji 「工」 or 「口」 or ... So it offers you its best "guess" (for example, which of the possible kanji you chose last time), followed by a handful or sometimes dozens of other kanji that also have that reading.
As an example, if I type (using Anthy)
ちょうし SPACE はどう
As you see, you don't have to convert every kanji separately. But an IME's ability to "understand" the hiragana input is limited. So, if tried to convert the above all at once with
But, for example,
gets correctly converted to
It's a matter of experience to judge what "portion" you can reasonable convert at once.