Thailand is 55% larger than Vietnam.
Area: 513,120 km2 World Factbook
Population: 67,741,401 (July 2014) World Factbook
Thailand, officially the Kingdom of Thailand, formerly known as Siam, is a country at the centre of the Indochina peninsula in Southeast Asia. Wikipedia
Area: 331,210 km2 World Factbook
Population: 93,421,835 (July 2014) World Factbook
Vietnam, officially the Socialist Republic of Vietnam, is the easternmost country on the Indochina Peninsula in Southeast Asia. With an estimated 90.0 million inhabitants as of 2013, it is the world's 13th-most-populous country, and the eighth-most-populous Asian country. Wikipedia