It also all depends on how a team drafts. Some teams have guidelines on what type of pitchers they draft. Some teams will only draft pitchers that are 6'-6'5, nothing less nothing more.
Velocity isn't everything as well. It's all about arm action, consistancy and projectability. If you have good arm action, a good body, and are 86-90 with your FB, you may have a chance. It all depends on who sees you. You may have 10 teams see you, 9 dont like you, 1 does. Like they say,"it only takes one team"
It also depends on how hitters react to your pitches, movement, how you change speeds, what you throw in different counts.
Perfect example, A high school pitcher who consistantly throws 84-88, but throws his CB 75,76 maybe 77 MPH, may be able to throw 90,91,92 someday.
HS guys who throw 90 plus consistantly with good stuff are generally going to have a good chance.
Nothing is a guarentee though, the draft is a funny thing.