A megacity is a metropolitan area with a population of 10 million or more, a threshold set by the United Nations. There are around 34 megacities in the world today, up from just two — New York and Tokyo — in 1950, and the UN projects that number will reach roughly 43 by 2030. Most are in Asia, and the fastest growth is now in Africa.
The megacity is a genuinely new kind of human settlement. For nearly all of history no city anywhere exceeded a million people; Rome may have touched that mark around 100 CE, and then nothing did again until London in the early 1800s. The jump from a million to ten million took place almost entirely within the last century, and the jump from two megacities to more than thirty took place within a single human lifetime.
The Definition — and Why It Is Slipperier Than It Looks
The 10 million threshold is simple. Measuring against it is not, because "a city" can mean three quite different things:
- The city proper — the area inside the municipal boundary. This is a legal definition and often bears little relation to the built-up reality. Paris proper holds about 2 million people; the Paris urban area holds over 11 million.
- The urban agglomeration — the contiguous built-up area, regardless of administrative lines. This is what the UN generally uses for megacity counts.
- The metropolitan area — the built-up area plus the surrounding zone economically tied to it through commuting. This is usually the largest figure.
The choice matters enormously. Chongqing in China is often listed as a megacity of over 30 million, but its municipality covers about 82,400 km² — larger than Austria — and most of that is rural; the actual urban core is far smaller. Conversely Jakarta's official city population understates a contiguous built-up region, Jabodetabek, of well over 30 million. This is why different reputable sources give different megacity counts and different rankings, and why any specific number should be read as approximate.
Where the Megacities Are
The distribution is strikingly uneven:
- Asia (roughly 22): Tokyo, Delhi, Shanghai, Dhaka, Beijing, Mumbai, Osaka, Karachi, Chongqing, Kolkata, Manila, Guangzhou, Tianjin, Bengaluru, Lahore, Shenzhen, Jakarta, Hyderabad, Seoul, Wuhan, Chengdu and Ho Chi Minh City.
- Americas (roughly 6): Mexico City, São Paulo, New York, Buenos Aires, Lima and Bogotá.
- Africa (3): Cairo, Lagos and Kinshasa.
- Europe (2): Moscow, and London on a metropolitan definition.
- Middle East (1): Istanbul, which straddles the European–Asian boundary.
Asia's dominance reflects both sheer population and the speed of its industrialisation. China has around eight megacities and India around five, and both lists are still growing as rural-to-urban migration continues. Notably absent is most of the wealthy world: Western Europe, North America outside New York and Mexico City, and Australia have very few, because their urbanisation happened earlier, more slowly, and with the car enabling low-density spread rather than extreme concentration.
Africa is the region to watch. It has only three megacities now but is urbanising faster than anywhere else on Earth. Kinshasa has grown from under half a million people in 1960 to well over 17 million; Lagos has grown roughly a hundredfold since 1950 and is projected to be among the world's very largest cities by mid-century. Reasonable projections put Africa at ten or more megacities by 2050. Our guides to Lagos and global urbanisation trends cover this shift in more detail.
How the Count Grew
- 1950: 2 — New York and Tokyo.
- 1975: 3 — Mexico City joins.
- 1990: around 10 — adding São Paulo, Osaka, Mumbai, Kolkata, Seoul and others.
- 2000: around 16.
- 2010: around 23.
- Today: around 34.
- 2030 (UN projection): around 43.
Three forces drove this. Falling mortality — better sanitation, vaccination and food supply — meant cities stopped being population sinks that required constant in-migration just to hold steady. Agricultural mechanisation released rural labour. And industrialisation plus, later, service-sector growth concentrated jobs in a small number of places. Where all three arrived at once and fast, as in East and South Asia after 1950, cities grew at rates that no earlier urban system had experienced.
What Concentration Buys — and Costs
Megacities exist because density has real economic value. Firms benefit from deep labour markets, dense supplier networks and the fast circulation of ideas — the agglomeration effects that make large cities disproportionately productive. Megacities generate roughly 15% of global GDP on about 2% of the world's population. Tokyo's metropolitan output exceeds that of all but a handful of entire countries.
The costs are equally geographic:
- Housing: informal settlements house something like 30–60% of residents in many developing-world megacities, because formal construction cannot keep pace with in-migration.
- Transport: commuting time rises sharply with size. Lagos commutes of three hours round-trip are common; Manila, São Paulo and Delhi all face severe congestion.
- Air quality: Delhi, Dhaka and Lahore regularly record particulate levels many times the WHO guideline, with measurable effects on life expectancy.
- Water: Mexico City has pumped groundwater so hard that parts of the city are subsiding by up to roughly 50 cm a year, cracking pipes and causing further losses. Chennai faces recurring summer shortages.
- Governance: megacities routinely span dozens of municipalities and multiple states or provinces, so no single authority controls the transport, water or housing system.
Megacities also concentrate inequality with unusual visibility. In Mumbai, the Antilia private residence stands within sight of Dharavi, one of Asia's largest informal settlements. In São Paulo, helicopter commuting developed specifically as a way for the wealthy to bypass gridlock that everyone else endures. That spatial juxtaposition is not incidental — it is what happens when extreme wealth and extreme scarcity of land occur in the same place.
Megacity vs Metropolis vs Conurbation: Getting the Terms Right
Several related terms describe large urban forms, and they are not interchangeable.
- Metropolis — a large, dominant city with its surrounding commuter zone. No fixed population threshold; a metropolis of 3 million is perfectly normal. Every megacity is a metropolis, but not vice versa.
- Megacity — specifically 10 million or more. A hard numerical threshold, applied to a single continuous urban area.
- Conurbation — several originally separate towns or cities that have grown into one another, so that the built-up area is continuous but there is no single historic core. The English Midlands around Birmingham and Germany's Ruhr are classic examples. A conurbation may or may not reach megacity size.
- Megalopolis — a much larger structure: a chain of metropolitan areas whose peripheries merge into a near-continuous urbanised corridor. The US Northeast from Boston to Washington is the original example, coined by geographer Jean Gottmann; China's Pearl River Delta and Japan's Taiheiyō belt are others. A megalopolis contains multiple metros and can hold 50 million or more.
- Global city — defined by function rather than size: a city that acts as a command point in the world economy. London and Zurich qualify on influence while being modest in population; Kinshasa is a megacity but not a global city.
The distinction that matters most in practice is megacity versus megalopolis. A megacity is one city that got very large. A megalopolis is many cities that ran into each other. They pose different planning problems: the first is about managing a single overloaded core, the second about coordinating across many independent authorities.
What Comes Next
The next phase of megacity growth is likely to look different from the last. Several governments are attempting to redirect growth rather than accommodate it in place. Egypt is building a new administrative capital east of Cairo; Indonesia is constructing Nusantara in Borneo partly because Jakarta is both sinking and congested; India has pursued a large "smart cities" programme. Whether purpose-built capitals actually absorb growth has a mixed historical record — Brasília and Abuja both succeeded politically while their originating cities kept growing anyway.
Meanwhile the most consequential investments are unglamorous: metro and bus rapid transit systems in Delhi, Dhaka, Lagos and Bogotá; sewerage and water treatment; land-titling that lets informal settlements be upgraded rather than cleared; and flood defence, since a disproportionate share of megacities sit on coasts or deltas. Mumbai, Shanghai, Dhaka, Jakarta and Lagos all face rising seas alongside intensifying storms, while inland Delhi and Cairo face heat extremes that increasingly exceed what their infrastructure was designed for.
Technology helps at the margins — adaptive traffic control, smart metering, leak detection — but the binding constraints on megacities are institutional rather than technical: who has authority over the metropolitan area, who can raise revenue, and whether land use and transport are planned together. Those are the questions that will determine living conditions for a growing share of humanity, since more than half the world's people already live in cities and the proportion continues to climb.