A Penetration report provides a count of customers next to the total universe count for a segment of a compiled file, and the ratio of the two numbers is the penetration the company has made into the market. For example,

Market	Universe	Customers	Penetration
Atlanta	80,150	4,456	5.56%
Boston	95,165	5,885	6.18%
Chicago	120,123	11,817	9.84%
Dallas	75,432	4,281	5.68%
Houston	54,546	3,228	5.92%
Miami	80,889	7,900	9.77%
New York	135,432	12,100	8.93%
Washington DC	101,896	10,123	9.93%
Other Markets	645,550	45,381	7.03%
Denver	29,883	15,552	45,435
Total	1,389,183	105,171	7.57%

Penetration reports can be two dimensional as well, and each report can reflect a subset of the entire universe. For example, the above report could reflect total households in each market, or only households with children.

Penetration reports are valuable ways of identifying the niches in the universe where there are real possibilities for expanding market share.