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.

There are also sources out there for using your torso measurement to determine (effective) top tube length. I suggest familiarity with what sort of fit you want as well.

Also, get someone to help measure you, if you can; it will be more accurate.

Professional, ? just go stand over some bikes in a Bike Shop, shopping is free.

There are no bike stores where I live..
I'm just doing this based off your guys experience.
78cm inseam - 47cm, 50cm, or 53cm frame?

Fit Calculator - Competitive Cyclist

Try the bikes. A 53 from one company may not be the same as a 53 from another company. For what it is worth, my inseam is a little shorter than yours and I ride a 57 cm Raleigh.

This is online. No bike stores are near me so I have to rely on internet calc's and bicycle experts on this one.

Specifically what bikes are you looking at? Do you have a link?

I am looking at the Mercier Kilo TT

I have a question.. what if my bicycle frame size is smaller than what I should be getting? According to resources.. I should be 50.7 cm (frame size 78 (inseam) x .65 (road bike) = 50.7)
So if I decided to get a 47 cm sized frame instead of a 50 cm sized frame.. what is the disadvantage?

Your anal charts, graphs, charts and figurings say that it won't work**********???

Rivendell Bikes has some pretty detailed information on Bike fitting.

https://www.rivbike.com/Articles.asp?ID=247

DO NOT buy a first road bike over the internet based on any fit calculations made independent of (a) the bike's unique geometry and sizing, and (b) a knowledgeable road bike rider to help you personally. Your chances of success aren't good. Worst that can happen? Your bike will not fit you and you'll spend additional money trying to optimize a bad situation with setback seatposts, shorter/longer stems, awkward rotation of the handlebars, etc.

You must be able to find a few bicycles to try. Do you have a local want ads or craigslist listing? Can you travel to one or two bikes for sale to try them? Can you make detailed notes about what works and what doesn't, and the corresponding measurements made accurately and repeatably between different bikes? Then, you might have a chance buying over the web later...

A bit small is better than a bit large.

If it feels too cramp, use a longer stem.

My inseam is 74cm and 49cm is my preferred size.

According to BD's sizing chart, the 50cm has a 52cm TT. The 47cm has a 51cm TT.

More likely, a 47cm is a good start for you. Just use a longer stem if it is too cramp.