How many open syllable gigantic?

Let's break down the word "gigantic" to find the open syllables:

* gi-gan-tic

Open syllables have a vowel sound followed by a consonant.

* gi is an open syllable.

* gan is a closed syllable (vowel followed by a consonant).

* tic is a closed syllable.

Therefore, there is one open syllable in the word "gigantic".