I'm going to prove that I am no math major with this statement, but it's 55" in diameter (I think that's the proper measurement - I hated high school geometry).
Don't feel bad, I only know about that stuff because thats how we measure our pizza pies here. klydon cleared it up (with his answer above). A 16" pie is, indeed, huge. Most of the ones I see around here are about 9" or 10" (and now I'm dying for one).
