My personal formula is a little bit more conservative than 6 months PITI, but my down payment funding plan is much more aggressive than average so I need to have additional cash on hand to balance the risk.

Everyone has a different formula, @Dong Yan.

Id also recommend Frank Gallinelli's book "What Every Real Estate Investor Needs To Know About Cash Flow" its super informative and talks about the real estate terms, definitions and lingo that we all need to know to function as RE investors as well as the math equations, formulas and rules of thumb that are also necessary in this game.  

I’m a relative newbie, cap rate has been one metric that I have spent a bit of time learning, partly because of the various definitions of it and the occasional misconceptions surrounding it.The formula I see all the time is Cap Rate = NOI/(Purchase or Value) which does not include leverage.

My question in regards to that is what formula or numbers can I use to make sure it would be a sound investment.  

Also if anyone has any spreadsheets or formulas they use that would be helpful!

See you are trying overlay a formula onto a property where it may or may not work.

Going with this formula it seems that it would take years before the properties where generating enough cash flow to save and buy another.

Your formula can work.

Are there any formula or any such thing?