Boise, Idaho is 3.1 times larger than Boulder, Colorado.
Area: 207 km2 calculated
Boise is the capital and most populous city of the U.S. state of Idaho, as well as the county seat of Ada County. Located on the Boise River in southwestern Idaho, the population of Boise at the 2010 Census was 205,671, the 99th largest in the nation. Its estimated population in 2013 was 214,237. Wikipedia
Area: 68 km2 calculated
Boulder is the county seat and most populous city of Boulder County and the 11th most populous city in the U.S. state of Colorado. Boulder is located at the base of the foothills of the Rocky Mountains at an elevation of 5,430 feet. The city is 25 miles northwest of Denver. Wikipedia