Nigeria is 3.8 times larger than Guinea.
Area: 245,857 km2 World Factbook
Population: 11,474,383 (July 2014) World Factbook
Guinea, officially the Republic of Guinea, is a country in West Africa. Formerly known as French Guinea, it is today sometimes called Guinea-Conakry to distinguish it from its neighbour Guinea-Bissau and the Republic of Equatorial Guinea. Wikipedia
Area: 923,768 km2 World Factbook
Population: 177,155,754 (July 2014) World Factbook
Nigeria, officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. Wikipedia