There are two numbers I often think and talk about, and find useful. One is the gross rent multiplier, the other is the cost of construction. Gross rent multiplier is the purchase price of the property divided by the total annual rent. Oftentimes, depending on your personal economics, management style, and management costs, a fully leveraged property (80% LTV) requires a 9 gross rent multiplier (for me) to break even including all things (mortgage, insurance, property tax (in my area), maintenance, capex, vacancy, etc.). The lowest gross rent multiplier for a market rate property (that I would actually be interested in purchasing) in my 20 year career was in the 11 range (again in my area). The cost of construction is another consideration when thinking about real estate. In my area the cost of construction is in the neighborhood of $250-$325/sq ft depending on quality of construction, excluding land.