Mongolia is 4.1 times larger than Japan.
Area: 377,915 km2 World Factbook
Population: 127,103,388 (July 2014) World Factbook
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. Wikipedia
Area: 1,564,116 km2 World Factbook
Population: 2,953,190 (July 2014) World Factbook
Mongolia is a landlocked country in east-central Asia. It is bordered by Russia to the north and China to the south, east and west. Ulaanbaatar, the capital and also the largest city, is home to about 45% of the population. Mongolia's political system is a parliamentary republic. Wikipedia