St. Petersburg, Florida is 15% larger than Gainesville, Florida.
Area: 145 km2 calculated
Gainesville is the county seat and largest city in Alachua County, Florida, and the principal city of the Gainesville, Florida Metropolitan Statistical Area. The population of Gainesville in the 2010 United States Census was 124,354. Wikipedia
Area: 166 km2 calculated
St. Petersburg is a city in Pinellas County, Florida, United States. As of the 2013 census estimate, the population was 249,688, making St. Petersburg the 5th most populous city in the state of Florida and the largest city in Florida that is not a county seat. St. Wikipedia