Africa is the world's second-largest and second-most-populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area and 20% of its land area. With 1.3 billion people as of 2018, it accounts for about 16% of the world's human population. Africa's population is the youngest amongst all the continents; the median age in 2012 was 19.7 when the worldwide median age was 30.4.