South and East Asia alone account for nearly half of humanity. Europe plus North America combined = ~12%.
Top 10 most populous countries (2025)
🇮🇳 India
1.44B · #1
🇨🇳 China
1.41B · #2
🇺🇸 USA
340M
🇮🇩 Indonesia
278M
🇵🇰 Pakistan
250M
🇧🇷 Brazil
216M
🇳🇬 Nigeria
230M
🇧🇩 Bangladesh
175M
🇷🇺 Russia
143M
🇪🇹 Ethiopia
130M
India overtook China as the most populous country in 2023. Nigeria is growing so fast it may enter the top 3 by 2100.
Part E · fertility, ageing, and demographic change
Replacement fertility rate
2.1 children
A population needs ~2.1 births per woman to stay stable. Below this = eventual shrinkage.
Global fertility rate (2025)
~2.3
Down from ~5.0 in 1950. Still above replacement globally, but well below in rich countries.
Countries below 2.1
> 100
Most of Europe, East Asia, and North America are already below replacement. Their populations age and eventually shrink.
Fertility rates around the world
Children per woman (total fertility rate). Dashed line = replacement level (2.1).
Niger
6.7
Highest in the world
Mali
5.9
West Africa
Chad
5.5
Central Africa
DRC
5.2
Central Africa
Angola
5.1
Southern Africa
Afghanistan
4.5
Central Asia
Sub-Saharan Africa will drive nearly all of global population growth in the 21st century.
India
2.0
Just below replacement
Indonesia
2.2
Southeast Asia
Mexico
2.0
Latin America
USA
1.7
Below replacement
Brazil
1.7
Below replacement
France
1.8
Highest in W. Europe
South Korea
0.72
Lowest ever recorded
Hong Kong
0.75
City-state extreme
Japan
1.2
Declining since 1975
Italy
1.25
Shrinking population
Germany
1.4
Depends on immigration
China
1.0
Peak population passed
South Korea's fertility rate of 0.72 means each generation is roughly ⅓ the size of the previous one.
The world's age structure — 100 people
Each dot = 1% of world population. Color = broad age group.
0–14 yrs (26%)
15–64 yrs (65%)
65+ yrs (9%)
By 2100, the 65+ share is projected to reach ~22%. The world is ageing fast.
Life expectancy at birth — selected countries (2025)
Japan
84 yrs
Switzerland
83.8 yrs
Australia
83.3 yrs
Germany
81.4 yrs
USA
77.5 yrs
Brazil
74 yrs
India
70 yrs
Global avg.
~73 yrs
Nigeria
55 yrs
Chad
53 yrs
In 1900 global average life expectancy was ~32 years. A 40-year gain in a single century is one of humanity's greatest achievements.
Part F · urbanisation — the great migration to cities
Urban population (2025)
~57%
More than half of humanity now lives in cities. In 1800 it was ~3%.
New urban residents/week
~1.5 million
Equivalent to a new Chicago appearing every week, worldwide.
Urban by 2050 (projected)
~68%
Most urban growth will occur in Asia and Africa. Europe and Americas already >75% urban.
Urban vs. rural split over time
1800
97% rural
1950
30%
70% rural
2007
50% — historic milestone
2025
57% urban
43% rural
2050
68% urban (proj.)
Largest megacities (2025, metro population)
1Tokyo, Japan
37M
2Delhi, India
36M
3Shanghai, China
29M
4Dhaka, Bangladesh
26M
5São Paulo, Brazil
25M
6Mexico City
22M
7Cairo, Egypt
22M
8Mumbai, India
21M
9Beijing, China
21M
10Osaka, Japan
19M
A "megacity" = city of 10M+. There are now 35 megacities globally, up from just 2 in 1950 (New York and Tokyo).
Part G · future projections — where are we headed?
Peak population (UN medium)
~10.4B
Expected around 2080–2100, then slow decline or plateau. Not runaway growth.
Growth rate today
~0.9%/yr
Down from a peak of 2.1%/yr in 1968. The absolute rate is still falling.
Africa's share by 2100
~40%
Africa is expected to hold ~4 billion people by 2100 — up from 1.4B today. The continent will define 21st-century demography.
UN population projections to 2100
Three scenarios: low, medium, and high fertility assumptions.
2025 (now)
8.2B
2050 (medium)
9.7B
2100 (low)
7.3B
2100 (medium)
10.4B
2100 (high)
15.8B ↑
The spread between low and high scenarios is enormous — everything hinges on whether fertility in Sub-Saharan Africa falls quickly or slowly.
The demographic dividend — why it matters
Young bulge
When birth rates fall, a country gets a large working-age population with fewer dependents
This window of high productivity drove East Asia's economic boom (South Korea, Taiwan, China, 1970–2000)
Africa now
Africa is entering this window — the world's youngest continent (median age ~19)
If governance and education improve, this could be the largest economic dividend in history
Ageing trap
Japan, South Korea, and parts of Europe have the opposite: too many elderly, too few workers
Japan has a 65+ share of ~30% — 1 in 3 people is retired. Pension systems face serious strain.
Part H · interactive — population calculator
How long until the next billion?
Adjust the annual net growth rate and see how long it takes to add another billion people to the current 8.2B.
Annual growth rate:0.9%
How many people have been born during your lifetime?
Your birth year:
Compare two countries
Country A
Country B
Part I · test yourself
1. How many people were alive when the Roman Empire was at its peak (around 100 AD)?
About 300–400 million total worldwide. That's less than the current population of the USA alone (330M). Today's world has 25× more people than existed then.
2. In one hour, how many babies are born worldwide?
About 16,000. (385,000 per day ÷ 24 hours ≈ 16,000 per hour.) In the time it takes to watch a movie, roughly 32,000 babies are born.
3. What percentage of all humans who ever lived are alive right now?
About 7.6%. With 8.2 billion alive and ~108 billion ever born: 8.2 ÷ 108 ≈ 7.6%. More humans are alive today than in any previous era — yet we're still less than 1 in 12 of everyone who ever existed.
4. The world gains 80 million people per year. Which country has a population close to that number?
Germany (~84M) or Turkey (~85M) are the closest. So the world adds roughly one Germany's worth of people every single year.
5. What is the "replacement fertility rate" and why is 2.1, not 2.0?
Replacement rate is the fertility level needed for a population to replace itself without immigration. It's 2.1 (not 2.0) because a small fraction of children don't survive to reproductive age and because slightly more boys than girls are born. The extra 0.1 accounts for this mortality buffer. In high-mortality countries, the replacement rate can be even higher (2.3–3.0).
6. South Korea has the world's lowest fertility rate of ~0.72. If that continued for 60 years, roughly what would happen to its population?
Each generation would be about 34% the size of the previous one (0.72 ÷ 2.1). Over three 20-year generations (60 years), the population would fall to roughly 0.34³ ≈ 4% of its current size. South Korea's 52M would shrink toward ~2M. This won't fully happen — immigration and policy changes are likely — but it illustrates the maths of sub-replacement fertility.
7. What major demographic event happened in 2007?
For the first time in human history, more people lived in cities than in rural areas. In 1800, only about 3% of people were urban. The 50% crossover in 2007 was a genuine turning point — humanity became an urban species.
8. By 2100 which continent is expected to hold the most people?
Africa. The UN medium projection has Africa reaching ~4 billion people by 2100 — roughly 40% of the global total. Today Africa holds ~1.4B (17%). This demographic shift will be the defining story of the 21st century, reshaping economics, migration, and geopolitics.