Baltimore's population is approximately 637,000 within the city limits.
Regarding Baltimore's metropolitan area:
The Baltimore-Washington Metropolitan Area is a combined statistical area consisting of the overlapping labor market region of the cities of Baltimore, Maryland and Washington, D.C.. The region includes Central Maryland, Northern Virginia, and two counties in the Eastern Panhandle of West Virginia. It is the most educated, highest-income, and fourth largest Combined Statistical Area in the United States.
The population of the entire Baltimore-Washington Metroplex as of 2007 is 8,241,912.
(Wikipedia)