The New King of Megacities: How Jakarta Quietly Became the Largest City on Earth

Jakarta is officially the largest city on the planet - 42 million people / Photo by Getty Images for Unsplash+

For decades, the answer to “what is the world’s biggest city?” was automatic. It was Tokyo. It was always Tokyo. That era is over.

Tokyo Steps Down

The UN’s “World Urbanization Prospects 2025” report, released in November 2025, is the first revision since 2018 – when Tokyo was the world’s largest city and Jakarta was ranked 33rd. Tokyo is now ranked third.

The city that dethroned it is Jakarta, the sprawling, chaotic, magnificent capital of Indonesia – and the speed of its rise is staggering. In seven years, it went from 33rd place to first. In a single UN reporting cycle, the entire geography of human urban settlement was redrawn.

With an estimated population of nearly 42 million residents, Jakarta soared to the top of a ranking increasingly dominated by Asia. It edged out Bangladesh’s capital Dhaka, with 36 million, and Japan’s Tokyo, now third with 33 million.

This is not merely a statistical curiosity. It is a signal about where the twenty-first century is being built, who is building it, and at what extraordinary cost.

The Numbers Behind the Number

Before going further, one clarification is essential – because the figures involved only make sense once you understand what they are measuring.

Jakarta’s official city population in 2025 is approximately 10.68 million people – a large city by any measure, but not exceptional on a global scale. The figure of 42 million refers to something considerably larger: the continuous urban agglomeration known in Indonesian as Jabodetabek – an acronym for Jakarta, Bogor, Depok, Tangerang, and Bekasi, the ring of satellite cities and suburbs that have grown into and around each other until the boundaries between them are largely invisible on the ground.

The UN’s new methodology measures urban populations based on contiguous urban agglomerations with at least 1,500 inhabitants per square kilometre – a definition that captures the real lived experience of a megacity more accurately than administrative borders drawn decades ago.

By this measure, the greater Jakarta region is home to 42 million people. That is roughly the population of Canada. If Jakarta were a European country, it would rank 8th in population out of 45 countries (the 44 existing ones + Jakarta), before Poland. It is a human concentration of a scale that is almost impossible to visualise.

To complete the picture of Asia’s demographic dominance: nine of the world’s ten most populated cities are now located in Asia. The only exception is Cairo, ranked seventh with 25 million – more than double the population of New York City.

Why Tokyo Fell and Jakarta Rose

The contrast between these two cities is a compressed history of demographic divergence in the twenty-first century.

Tokyo may not have held the top position for a decade or two. Using updated definitions of urban extent, the UN report predicts Tokyo will fall further down the rankings in coming decades as population decline accelerates.

Forecasts project Tokyo’s urban population will decline from 33.4 million in 2025 to “only” 30.7 million by 2050, dropping its global rank to seventh.

Japan is ageing at a pace that demographers describe as without modern precedent. A low birth rate, a deep cultural resistance to immigration, and a shrinking workforce are combining to produce a city that is not merely growing more slowly – it is beginning to contract. Tokyo in 2050 will be smaller than Tokyo today.

Jakarta is the opposite story in almost every respect. Indonesia is a young country – its median age is around 30, compared to Japan’s 49 – with a growing middle class, rapid urbanisation, and the economic momentum of Southeast Asia’s largest economy.

People are moving to Jakarta, and to the cities within Jabodetabek, because that is where the jobs, the hospitals, the universities, and the opportunities are. The tide of internal migration that built the megacity shows no sign of reversing.

The authors of the UN report noted that over the past quarter-century, the population of Tokyo has grown more slowly than the populations of Jakarta and Dhaka, leading to its drop in rank – a trend expected to continue over the coming decades.

And Jakarta’s reign at the top may itself be temporary. Jakarta is followed by Dhaka, with 36 million, which the report says is expected to become the world’s largest city by mid-century – projections suggesting Dhaka could reach 52 million residents by 2050.

The Dark Side of the Record

To wear the crown of the world’s largest city in 2026 is not an uncomplicated honour. It comes with a set of infrastructure, environmental, and existential challenges that make Jakarta’s achievement inseparable from its crisis.

The Traffic That Eats Time

Jakarta has been consistently ranked among the most traffic-congested cities on Earth. The road network was built for a city of a few million and has been stretched, widened, elevated, and tunnelled without ever quite catching up to the demand of 42 million people trying to move simultaneously.

The economic cost is not rhetorical: hours lost in commutes, goods delayed in supply chains, fuel burned in stationary vehicles. It accumulates at a scale that measurably suppresses the city’s economic potential.

The Mass Rapid Transit system, opened in 2019 and expanded since, represents the most serious attempt yet to change the city’s fundamental relationship with its own geography. It is a genuine achievement. It is also, by the standards of what Jakarta needs, a beginning.

The Air Above and the Water Below

Air quality in Jakarta regularly exceeds WHO safe limits, driven by vehicle emissions, coal-fired power, and the sheer density of industrial and domestic activity compressed into the agglomeration.

On bad days – which correlate with weather patterns that trap pollutants over the city – the air index reaches levels that medical authorities classify as hazardous.

Water management presents its own layered crisis. The 13 rivers that flow through Jakarta carry the waste of the surrounding region into the heart of the city.

Flooding during the rainy season is not an occasional emergency but an annual expectation, affecting millions of residents in low-lying areas that return to water every year.

The Groundwater Trap

Here the problems compound each other in a way that is technically fascinating and practically catastrophic.

The National Research and Innovation Agency says parts of Jakarta are sinking by 10 to 30 centimetres every year, driven by natural soil compaction and decades-long overuse of groundwater by homes, businesses, and industries. The subsidence rate is among the fastest of any major city in the world.

The mechanism is straightforward and brutal: millions of people and thousands of businesses extract groundwater from the aquifers beneath the city because the piped water supply is insufficient.

As the water is removed, the soil above compacts. The land sinks. The aquifer, now compromised, allows seawater intrusion from the coast. The groundwater becomes saltier, less usable, which drives more extraction from deeper sources, which causes more sinking.

Jakarta is sinking fast due to heavy groundwater use and rapid urban growth, leaving 40% of the city below sea level and worsening floods.

The City That Is Disappearing Into the Sea

The convergence of land subsidence and rising sea levels has produced a situation in Jakarta that has no comfortable framing.

Field observations have shown sea levels at Pantai Mutiara in North Jakarta overtopping the height of surrounding land, held back only by a coastal embankment. Without these barriers, seawater would flow inland.

The coastal area of North Jakarta has sunk 2.5 metres in the past decade and continues to do so at the rate of 25 centimetres per year. Some areas of the city have sunk more than four metres since the 1970s.

Parts of North Jakarta that were productive urban land within living memory are now effectively sea defence projects, maintained against the ocean by embankments rather than by geography.

Jakarta loses at least US$186 million annually due to flood risks – a figure projected to rise to $421 million by 2030 if subsidence continues unabated.

The dangerous combination of rising waters and sinking land means Jakarta will likely be partly submerged by 2050 if no action is taken. This is not an alarmist projection.

It is the working assumption of the Indonesian government – which is why, in 2019, it made one of the most dramatic planning decisions of the twenty-first century.

Nusantara: The Escape Plan

The decision to move Indonesia’s capital from Jakarta to an entirely new city on the island of Borneo is, depending on your perspective, either a visionary act of national planning or an admission of defeat. It is probably both.

Plans to build the city of Nusantara were first announced in 2019 by former Indonesian president Joko Widodo, who wanted to relocate the fast-sinking Jakarta. Located on the east coast of the island of Borneo, Nusantara is set to become Indonesia’s political capital in 2028.

The project has not proceeded without complications. State funding for Nusantara has dropped since president Prabowo Subianto was sworn in in October 2024, falling from £2 billion in 2024 to £700 million in 2025, with £300 million allocated for 2026.

The new president has also adjusted the city’s designation: Prabowo downgraded Nusantara from Indonesia’s national capital to political capital in September 2025.

With the completion of the Vice Presidential Palace in January 2026, the Office of the Vice President has begun the relocation process to Nusantara.

President Prabowo has ordered the relocation of 1,700 to 4,100 civil servants to Nusantara within 2026, in order to achieve the required target of readiness for Nusantara as national capital in 2028.

The timeline, the funding, and the ultimate scope of Nusantara remain genuinely uncertain. What is not uncertain is the underlying reasoning: Jakarta, as a capital city, is physically running out of the geological stability that a capital city requires.

Jakarta After the Move

Here is the misunderstanding that the Nusantara story tends to produce in international coverage: the idea that Jakarta is being abandoned. It is not. It cannot be. You do not abandon 42 million people.

Jakarta will remain, regardless of what happens to Nusantara, the economic, financial, and commercial engine of the Indonesian archipelago – a nation of 280 million people, the fourth most populous on Earth, and one of the fastest-growing major economies in the world.

The headquarters of Indonesia’s largest companies, its ports, its manufacturing base, its financial institutions – none of these move because the president’s office moves to Borneo.

What Jakarta loses, if the transfer happens, is the specific burden of also being a political capital: the government ministries, the diplomatic missions, the bureaucratic infrastructure that adds millions of daily commuters to a city already straining under its own weight.

What it gains – potentially – is the space and the political will to address its existential infrastructure challenges without the competing demands of running a national government from the same postcode. Whether that proves to be enough is the question that will define Jakarta’s next half-century.

The Lesson in the Numbers

Nearly half of the planet’s 8.2 billion people now live in cities – more than double the urban share in 1950. Between 2025 and 2050, an estimated two-thirds of the world’s population growth is expected to occur in cities.

Jakarta is not an outlier. It is the leading edge of a wave. The megacities of Asia – Jakarta, Dhaka, Delhi, Manila, Kolkata – are accumulating population at a pace that the physical infrastructure of the twentieth century was not designed to absorb.

The challenges that Jakarta faces today – sinking ground, contaminated water, air quality crises, infrastructure overwhelmed by demand – are previews of what other rapidly urbanising cities will face in the decades ahead.

“Urbanisation is a defining force of our time. When managed inclusively and sustainably, cities can drive innovation and prosperity,” UN DESA noted in releasing the 2025 report.

The word “managed” carries enormous weight in that sentence. Jakarta’s experience suggests that the gap between the pace of urban growth and the capacity of urban governance to manage it is one of the defining challenges of this century.

The title of world’s largest city is no longer simply a point of civic pride. It is a measure of complexity, of pressure, of the scale at which human beings are now attempting to organise themselves on a planet that is simultaneously warmer, wetter, and less geologically stable than the cities built upon it were designed to accommodate.

Tokyo’s reign lasted for decades. Jakarta’s may be shorter. Dhaka is waiting.