Japan is an archipelago comprising 6,852 islands of which only around 430 are inhabited. The land area of Japan is 377,975 square kilometres (km2) (145,937 sq mi). The 5 main islands of Japan are, in order of land area – largest to smallest, Honshu, Hokkaido, Kyushu, Shikoku and Okinawa.

Their respective sizes are Honshu 227,960 km2 (88,020 sq mi) - the largest and most populous island with the capital Tokyo, Hokkaido 83,424 km2 (32,210 sq mi), Kyushu 36,782 km2 (14,202 sq mi), Shikoku 18,800 km2 (7,300 sq mi) and Okinawa 1,207 km2 (466 sq mi). The total land area of the first four of these 5 main islands amounts to 366,966 km2 (141,732 sq mi) which is 97.4% of Japan’s total land area.

More Info: en.wikipedia.org