Afghanistan is 4.6 times larger than Tajikistan.
Area: 652,230 km2 World Factbook
Population: 31,822,848 (July 2014) World Factbook
Afghanistan, officially the Islamic Republic of Afghanistan, is a landlocked country located in Central Asia and South Asia. It has a population of around 31 million people making it the 42nd most populous country. Wikipedia
Area: 143,100 km2 World Factbook
Population: 8,051,512 (July 2014) World Factbook
Tajikistan, officially the Republic of Tajikistan, is a mountainous landlocked country in Central Asia. It is bordered by Afghanistan to the south, Uzbekistan to the west, Kyrgyzstan to the north, and China to the east. Mountains cover more than 90% of the country. Wikipedia