Serbia is 5.6 times larger than Montenegro.
Area: 13,812 km2 World Factbook
Population: 650,036 (July 2014) World Factbook
Montenegro is a country in Southeastern Europe. It has a coast on the Adriatic Sea to the south-west and is bordered by Croatia to the west, Bosnia and Herzegovina to the northwest, Serbia to the northeast, Kosovo to the east and Albania to the south-east. Wikipedia
Area: 77,474 km2 World Factbook
Population: 7,209,764 (July 2014) World Factbook
Serbia, officially the Republic of Serbia, is a country located at the crossroads of Central and Southeast Europe, covering the southern part of the Pannonian Plain and the central Balkans. Wikipedia