San Francisco is 81% larger than Arlington County, Virginia.
Area: 67 km2 calculated
Arlington County is a county in the Commonwealth of Virginia. It is coterminous with the U.S. Census Bureau-designated place of Arlington, which is the second-largest principal city of the Washington, D.C. metropolitan area. Wikipedia
Area: 122 km2 calculated
San Francisco, officially the City and County of San Francisco, is the cultural center and a leading financial hub of the San Francisco Bay Area and Northern California. Wikipedia