How many letters in the Hawaiian alphabet?

Officially the written form of Hawaiian has 13 letters (a,e,i,o,u,h,k,l,m,n,p,w, and (') the 'okina). The 'okina is a glottal stop and is considered a consonant; without it the meaning of a Word is changed (ie "ko'u", meaning "my" and "kou" meaning yours)

Some instructors will tell you that there are in fact 10 vowels (a,e,i,o,u,ā,ē,ī,ō,ū).