Africa’s urban story is full of fast growth, rival claims, and statistics that shift depending on where you draw city lines. People often ask for a single winner, but the “biggest” label changes with the measure you choose.
If you mean the largest by population in the commonly used metropolitan sense, Lagos, Nigeria is widely cited as the biggest city in Africa, with estimates often in the low-to-mid 20 millions; if you mean the largest by population inside official municipal boundaries, Cairo, Egypt is frequently the leader at roughly 10 million within the city proper, while its wider urban region is far larger.
1) What “biggest” means: city proper vs. urban area vs. metro
The simplest count is “city proper”: the population inside an administrative boundary. This can understate size when a city spreads far beyond the legal limits, which is common in rapidly expanding regions.
An “urban area” typically measures the continuous built-up footprint—where the city’s density is physically connected. A “metropolitan area” usually adds surrounding commuter zones that are economically tied to the core. These definitions explain why two sources can both be correct while giving different answers.
In Africa, boundary effects are dramatic. Lagos has a relatively small official city area compared with its real-world sprawl into adjoining districts, while Cairo’s administrative city count is substantial but still smaller than the total population of the Greater Cairo region that includes Giza and other surrounding governorates.
2) Lagos: the frequent answer for Africa’s largest metro population
Lagos is often named the biggest city in Africa because its metropolitan population is estimated in the tens of millions, with many demographic projections placing it above 20 million. It is Nigeria’s commercial powerhouse, built around a lagoon system and a dense coastal corridor that has expanded outward along highways and into satellite towns.
Concrete contrasts make Lagos stand out: its growth has been fueled by internal migration from across Nigeria and neighboring countries, a very young population, and the pull of jobs in trade, services, entertainment, and ports. The city’s economy is diversified—from markets and manufacturing to finance and technology—yet the pace of in-migration often outstrips infrastructure delivery, creating intense demand for housing, transport, water, and power.
Because the urban footprint crosses multiple administrative units, Lagos illustrates why “city proper” counts can mislead. A narrow legal boundary might suggest a smaller city, while everyday experience—commutes, housing estates, industrial zones, and continuous development—reveals a huge metropolitan organism.
3) Cairo (and other contenders): different metrics, different winners
Cairo is a top contender depending on the definition. The city proper is commonly reported around 10 million people, and the broader Greater Cairo region—often including Giza and surrounding areas—ranks among Africa’s largest urban agglomerations. Its density, long-established institutions, and role as a political and cultural center create a different urban profile from newer, faster-spreading metros.
Other large African cities also challenge for “biggest” under certain lenses. Kinshasa in the Democratic Republic of the Congo is frequently placed among the continent’s top few by urban population and is notable for rapid growth and vast geographic spread along the Congo River. Johannesburg’s wider urban region (including parts of Gauteng) forms one of Africa’s largest economic areas, though its population rankings depend heavily on which metro definition is used.
The key takeaway is that rankings are not just trivia: they affect planning and policy. A city that appears smaller on paper may still need mega-city solutions for transit, sanitation, and housing if its functional urban area is enormous. Conversely, a city with a large administrative count may still rely on regional coordination to manage water, air quality, and commuting flows.
Conclusion
Asked for a single name, Lagos is widely cited as the biggest city in Africa by metropolitan population, but Cairo often leads in city-proper counts and remains among the continent’s largest urban regions; the “right” answer depends on whether you measure legal boundaries, continuous built-up area, or the full metro economy.