It contains 28 letters. Check here : http://www.arabic-alphabet.org/

basically 28. in practice, you can find some form of 8 more.

only 28 letters every letter have 10 sounds b is one letter we can form ten sounds from it like this: ba, bo, be, baa, boo, bee, ban, bon, ben, ab. "الحرف "ب الأصوات هي: بَ ، بُ ، بِ ، با ، بو ، بي ، بًا ، بٌ ، بٍ ، بْ

29 letters with the letter " ء"