Picture standing on a train platform where people stretch as far as you can see, or looking out from a tower and seeing buildings all the way to the horizon. That’s what life feels like in the largest cities in the world.
But when someone asks, “What is the largest city in the world?” there’s a trick hidden in the question:
Are we counting people?
The official city?
Or the whole metro area that spreads into suburbs and nearby towns?
Let’s unpack that in kid-friendly language and figure out which city really comes out on top.
What Is the Largest City in the World by Population?
Most people searching for the largest city in the world are really asking:
Which city has the most people living in and around it?
When we count the entire metropolitan area (the city plus its connected suburbs and commuter towns), recent 2025 data still shows Tokyo, Japan as the largest city in the world by population, with around 36–37 million people in the greater Tokyo metro area.
Close behind are other huge megacities like Delhi, Shanghai, Dhaka, and Cairo, each with populations over 20 million.
So a simple, honest answer is:
Tokyo is currently the largest city in the world by population when you count the whole metro area.
Turn That Answer Into a Homework Win
If your learner is doing a geography or social-studies project on big cities, the kid-safe DIY.org AI Homework Helper can help them:
Turn “largest city in the world” into a clear outline
Explain tricky terms like metro area and megacity
Check that their explanation is in their own words
City vs Metro Area vs “Urban Area” (Why Lists Don’t Always Match)
Before we go deeper, it helps to know three terms that show up in rankings:
Term | Simple Definition | What It Includes | Why It Matters / Example |
City proper | The area inside the official city boundary set by law. | Just the legally defined city area. May include some rural land or separate towns, depending on how the boundary is drawn. | Lists using city proper can look strange: e.g., Chongqing in China has a huge boundary that covers lots of rural land. |
Metropolitan area (metro area) | The wider region built around a main city. | - The main city - Surrounding suburbs - Nearby towns strongly linked by jobs, commuting, and services | When you read that Tokyo has around 36–37 million people, that number is for the metro area, not just the central wards. |
Urban area | The continuous built-up zone where buildings and streets connect without big gaps of countryside. | All connected city-like space, even if it crosses official city borders. | Some rankings prefer this because it reflects how people actually experience “the city” in real life, not just legal boundaries. |
Different lists might use city proper, metro area, or urban area, which is why “largest city in the world” doesn’t always show the same winner.
Top 10 Most Populated Cities in the World (2025, by Metro Area)
Using recent 2025 metro-area data, the top 10 largest cities in the world by population look roughly like this:
Tokyo, Japan – ~37 million
Delhi, India – ~34–35 million
Shanghai, China – ~30 million
Dhaka, Bangladesh – ~24–25 million
Cairo, Egypt – ~23 million
São Paulo, Brazil – ~23 million
Mexico City, Mexico – ~22–23 million
Beijing, China – ~22–23 million
Mumbai, India – ~22 million
Osaka, Japan – ~19 million
You can see some patterns:
Many of the biggest cities in the world in 2025 are in Asia (Tokyo, Delhi, Shanghai, Dhaka, Beijing, Mumbai, Osaka).
Others are in Latin America and Africa (São Paulo, Mexico City, Cairo).
These mega-sized urban areas are where a huge portion of humanity now lives, studies, and works.
What Is a Megacity?
You’ll see the word megacity a lot in articles and textbooks.
Simple definition for kids
A megacity is usually defined as a city or urban agglomeration with more than 10 million people.
According to recent lists, there are now 40+ megacities worldwide, and most of them are in Asia and Latin America, with a growing number in Africa.
Where are the megacities?
If you place them on a world map, you’ll see clusters around:
East and Southeast Asia – Tokyo, Shanghai, Beijing, Guangzhou–Shenzhen, Seoul
South Asia – Delhi, Mumbai, Dhaka, Karachi, Kolkata
Africa – Cairo, Lagos, Kinshasa
Latin America – São Paulo, Mexico City, Buenos Aires
North America & Europe – New York, Los Angeles, London, Moscow
These megacities act like super-sized hubs for culture, finance, technology, and migration.
What Is Daily Life Like in the World’s Largest Cities?
Tokyo: The world’s biggest city by population
Tokyo is a good example of a dense, highly organized megacity:
Trains and subways run with tight schedules and carry millions of passengers each day.
Many people live in small apartments, but the city is packed with parks, shrines, tiny restaurants, and shops tucked into every corner.
The greater Tokyo area stretches across multiple prefectures far beyond what tourists think of as just “Tokyo city.”
Other megacities: Delhi, Shanghai, Dhaka, Cairo
Each megacity has its own personality:
Delhi – busy streets, historic monuments, a mix of planned neighborhoods and informal settlements, and a fast-growing population.
Shanghai – futuristic skyline, massive port, and a role as one of China’s financial and tech centers.
Dhaka – incredibly dense, with factories, markets, and neighborhoods stacked close together, and huge population growth.
Cairo – North Africa’s largest city, with ancient sites like the pyramids nearby and modern districts stretching along the Nile.
The good and the challenging sides of huge cities
Upsides:
More schools, universities, and museums
Better access to jobs, hospitals, parks, and public transit
Lots of chances to meet people and explore new cultures
Challenges:
Traffic jams and long commutes
High housing costs and crowded neighborhoods
Pollution and waste that are hard to manage at such a large scale
Megacities are places of intense opportunity and big problems all at once.
Compare Cities Like a Pro
If your learner wants to compare Tokyo vs Delhi vs your own city, they can ask the DIY.org AI Homework Helper to:
Build a comparison table (population, continent, language, climate)
Create Venn diagrams showing what the cities share and how they differ
Suggest questions for interviews, surveys, or class presentations
How Do We Count People in a City?
It sounds simple to say “Tokyo has 37 million people,” but that number comes from careful work.
Census and estimates
Countries run a census every so often, counting how many people live in each region.
Between censuses, researchers and organizations create population estimates based on births, deaths, and migration.
Why numbers don’t always match
If you see different population numbers in different places, check:
What year is the data from?
Are they counting the city proper, the metro area, or the urban area?
For example:
Tokyo’s 23 central wards have around 9–10 million people.
The broader Tokyo metropolis has over 13 million.
The whole Greater Tokyo metro area (the part that makes it #1 in the world) is around 36–37 million.
Teaching kids to ask “What exactly are we counting?” is a great critical-thinking habit.
Kids’ Corner: Map and Megacity Projects
This topic is perfect for hands-on geography and map skills.
Make your own “largest city in the world” map
Have kids:
Draw or print a world map.
Mark the top 10 most populated cities and label them.
Color-code by population (for example, 10–20M, 20–30M, 30M+).
To build those mapping skills, pair it with Cartography Activities for Kids on DIY.org. Kids learn how to read and create maps using symbols, colors, and keys.
Design your own megacity of the future
Ask: If you could design a megacity from scratch, what would it look like?
Where would the parks go?
How would people get around bikes, trains, electric buses?
Where would schools, hospitals, and homes be?
Then:
Use cardboard, blocks, or digital tools to build it out.
Try the Build a City of the Future challenge to turn sketches into a real model.
Map your own neighborhood first
Before kids think about Tokyo, they can understand their own city or town by mapping:
Their home
School
Park
Library
Favorite shops or sports field
The Map Your Neighborhood challenge walks them through how to plan, draw, and label a local map.
Draw a megacity skyline
For artsy kids, try:
How to Draw a City – then choose Tokyo, Shanghai, or your dream city as inspiration.
Turn Curiosity Into a Full Project
When your learner is ready to turn their research into a poster, slideshow, or report, the DIY.org AI Homework Helper can help them:
Rewrite notes in their own words
Plan sections (introduction, maps, megacity examples, conclusion)
Create quiz questions and captions for maps or diagrams
FAQ: Biggest City in the World (Kid-Friendly Q&A)
What is the largest city in the world by population right now?
Tokyo, Japan, is typically ranked the largest city in the world by metro population, with around 36–37 million people in 2025.
What is the most populated city in the world by 2030 or in the future?
Some projections suggest Delhi and other fast-growing cities in South Asia and Africa could eventually overtake Tokyo, as Japan’s population ages and growth slows.
How many megacities are there?
Recent studies list 40+ megacities (urban areas with more than 10 million people), and that number is expected to rise as urbanization continues.
Is the biggest city always the capital of its country?
Not always. Tokyo, Delhi, Cairo, and Mexico City are capitals and megacities. But huge cities like São Paulo or New York City aren’t national capitals.
What We Learn from the World’s Largest Cities
The key takeaways for kids: The largest city in the world by population is Tokyo, when you look at the entire metro area. A megacity is a city with more than 10 million people, and there are dozens of them now, especially in Asia and Latin America. Understanding city vs metro area vs urban area helps make sense of rankings that look different at first glance.
Most importantly, megacities show us how humans can cluster together in enormous numbers sharing ideas, solving problems, and sometimes creating new ones. Today’s kids who learn how these giant cities work may be the ones who design cleaner, greener, more livable cities in the future.
