Frame sizing formulas will not give you an exact frame size, because one bike company's 54cm is another's 56cm, or 55cm for a third company (I'm 5'9" with a 32.5" inseam, and I usually end up riding 54-55cm frames, but with the sizing some companies use, I end up riding 52-53cm's instead). All the formulas are good for is getting you into the ballpark that you should be looking into. The best way to determine size is to get fitted in person with a professional or at your LBS.