Largest City – How We Define the Biggest City on Earth

When you hear "largest city" you probably think of a place with millions of people, skyscrapers, and endless traffic. But "largest" can mean a few different things. Some count the number of residents, others look at how much land the city covers, and a few combine both ideas. Knowing which method is used helps you understand why one city might be called the biggest while another claims a bigger land area.

First, let’s clear up the two main ways to measure size. The most common metric is the population inside the official city limits. That tells you how many people live under one municipal government. The second metric is the urban or metropolitan area, which includes suburbs and nearby towns that function as a single economic zone. Both numbers matter, and they can paint very different pictures of a city’s reach.

How We Measure City Size

Population counts come from censuses and estimates that governments release every few years. These numbers are fairly reliable for an official city boundary, but they miss commuters who travel in daily from surrounding areas. To capture that, analysts use the concept of a metropolitan statistical area (MSA) or urban agglomeration. They add up all the people living in the surrounding suburbs that share jobs, transportation, and services with the core city.

Land area is another angle. Some cities sprawl over thousands of square miles, especially in places like the United States where zoning encourages spread. Others pack a massive number of residents into a compact space, as you see in many Asian megacities. When you combine population and land size, you get population density, which tells you how crowded a place really feels.

World’s Biggest Cities Today

By population inside city limits, Tokyo tops the list with over 13 million residents, while its broader metro area holds more than 37 million people. Delhi, Shanghai, and São Paulo also rank high, each housing tens of millions. If you look at land area, cities like Houston and Jacksonville in the US cover massive territories but have lower densities.

Megacities—urban areas with over 10 million people—are growing fast. Rising migration, higher birth rates, and economic pull make them expand both outward and upward. This growth brings challenges: traffic jams, housing shortages, and strain on utilities. Yet these cities also drive innovation, culture, and job creation.

Understanding what makes a city the "largest" helps you compare places fairly. Whether you’re planning travel, studying economics, or just curious, look at both population and area. That way you’ll see the real scale of the urban world and why some cities dominate the headlines while others quietly expand behind the scenes.