Hey guys, not sure if this is the correct place to post this...

My inseam is 78cm and I'm not sure what frame size I should get.
I've been told that you multiply your inseam by .65 for road bicycles and that will be your frame size.
I have also been told that you subtract a couple centimeters or add a couple...

Should I get a 47cm, 50cm, or 53cm bicycle frame?

P.S.

I can't get this done by a professional as I live no where near one.