Top Countries — Most Populous

Indonesia, with 284.4 million people, is Southeast Asia's largest archipelagic nation and demographic anchor, though its growth rate has slowed to 1.1% annually—three times faster than #3 United States but down from 1.5% a decade ago.

With a median age of just 22.7 years, the country's demographic trajectory is markedly younger than Nigeria's median of 18.1 years, fueling continued expansion. This rapid growth positions Pakistan to become the fourth-most populous nation worldwide by mid-century, adding roughly 4.5 million people annually. The population density of 287 people per square kilometer underscores the pressure on infrastructure, yet the fertility rate of 3.4 births per woman remains above replacement level. Without significant economic shifts, Pakistan's momentum will likely reshape regional demographics, outpacing slower-growing neighbors like Bangladesh.

Its median age of 18.1 years is the lowest on this list, driving a youthful expansion that adds roughly 5.4 million people yearly. This explosive growth outpaces the average global population growth rate of 0.9% by nearly threefold, yet the fertility rate has declined from 6.4 in 1980 to 5.1 births per woman. If current trends hold, Nigeria's population will double to over 400 million by 2050, reshaping global rankings and straining urban infrastructure in megacities like Lagos.

Brazil, with 213.4 million people, has seen its population growth slow to just 0.4% annually, causing it to slip from fifth place a decade ago to seventh, edging past Bangladesh by a margin of 43.6 million. Its fertility rate of 1.6 births per woman is now below replacement level, a stark contrast to Nigeria's 5.1 rate, and the median age of 33.5 years reflects an aging population. As the largest country in South America, Brazil's demographic shift is evidenced by a net migration loss of roughly 200,000 people yearly, further suppressing growth. Without a reversal, Brazil's share of the global population will continue to shrink, dropping below 2.5% by 2050, while fast-growing African nations ascend.

Bangladesh, with 169.8 million people packed into 147,570 square kilometers, is one of the world's most densely populated nations at 1,150 people per square kilometer, yet its fertility rate has plummeted to 2.0 births per woman, below Pakistan's 3.4. This demographic transition means growth is slowing to 1.1% annually, but the country's small land area magnifies challenges. Despite a median age of 27.3 years, Bangladesh's population is projected to peak at around 200 million by 2050, then decline, a trajectory far different from Nigeria's relentless expansion. The density, 30 times higher than Brazil's 25 people per square kilometer, underscores the pressure on resources, even as improvements in healthcare have pushed life expectancy to 74.5 years.

Russia’s 146 million inhabitants inhabit a staggering 17 million square kilometers, giving it by far the lowest population density among the top ten—just 8.6 people per square kilometer. Despite its ninth-place population rank, no other populous nation spreads its citizens so thinly, a distinction that shapes economic activity and infrastructure.

Its growth defies the trend seen in Japan, which dropped to eleventh due to a 0.2% annual population decline, whereas Mexico’s 0.8% growth rate ensures its spot on this list remains secure. This data highlights Mexico’s demographic vigor compared to aging rivals.