Calculator like that is basically for someone who doesn't know fuckall about what size board they need. It's a ballpark, best guess, based on some simple assumptions.
Suggests for me size 163-165 for all-mountain, which is longer than I'd ride except maybe for pow (although it's pretty accurate if you're assuming non-blunted, traditional camber). It suggests 159-161 for freestyle, which is longer than I ride (sweet spot for me is about 157).
Not saying the calculator doesn't have a purpose, but it ain't going to help you figure out if a 151 Draft is right for you.