The buy vs rent ratio is the cost of a typical home divided by the annual rent for a typical home.
The New York Times provides an updated list of the ratios for 55 US metropolitan areas. Chicago’s ratio is 16.6, about 10% above the national average of 15.1.
According to the Times article:
A good rule of thumb is that you should often buy when the ratio is below 15 and rent when the ratio is above 20. If it’s between 15 and 20, lean toward renting — unless you find a home you really like and expect to stay there for many years.
A metro-wide ratio isn’t very meaningful. Apply the rule of thumb to the properties that you’re typically interested in buying or renting.