There are two school of thought in this regard. Some claim that there are 29 letters keeping in view to particular shape and form. They do not count Alif and Hamza as one letter but two separate letters. Other say that there are 28 letters in Arabic alphabet and they count Alif and Hamza as one with an explanation that both will produce identical sound if they carry a stroke. In conclusion we can say that if look from s particular sound perspective, yes then 28 letters are correct but if we consider it from shape and form that we can identify 29 letters in Arabic spellings.