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The 50 Largest Urban Agglomerations in Europe (2025)

Victor Huber

2025-12-09

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Europe has some of the most beautiful, historic and vibrant cities in the world. However, almost every popular ranking of “the biggest cities in Europe” is based only on official administrative boundaries, often drawn a hundred or more years ago. These lists tell only part of the story.

The real size of a modern metropolis is revealed when we measure the urban agglomeration (also called Functional Urban Area): the continuously built-up area together with all surrounding municipalities whose inhabitants commute daily to the core for work, education or services.

What exactly is an urban agglomeration?

An urban agglomeration (or Functional Urban Area in Eurostat/OECD terminology) is:

• A core city or cities
• All surrounding municipalities that are physically built-up and connected
• Plus the commuter belt where at least 50 % of the employed population works in each municipality commutes to the core

In short: it measures the real living city, not the bureaucratic one.
That’s why Greater Paris has 11+ million people while the administrative City of Paris has only 2.1 million, and why the polycentric Silesian metropolis suddenly jumps into the European top 25.

The 50 Largest European Urban Agglomerations in 2025

Population figures are based on the latest harmonised Eurostat–OECD Functional Urban Areas dataset (2024–2025 update), UN World Urbanization Prospects, national statistical offices and morphological delimitations.

Five fascinating facts from the list

1. The Ruhr is the largest purely polycentric agglomeration in the world – no single city dominates; six cities over 500 000 live practically next door to each other.
2. Upper Silesia (Katowice agglomeration) is the largest urban area in Central Europe after Berlin, Budapest and Warsaw – larger than Vienna, Prague or Bucharest.
3. Greater Istanbul is the only European agglomeration that spans two continents.
4. If you added up every single municipality in the Dutch Randstad (Amsterdam + Rotterdam + The Hague + Utrecht), it would be Europe’s third-largest agglomeration with over 8 million people – but because it is polycentric, it never appears as one entry in classic rankings.
5. London and Paris are the only two Western European agglomerations that still grow mainly by natural increase (more births than deaths); almost everywhere else growth is driven by migration.

Sources & Methodology

This ranking uses the Functional Urban Area (FUA) / morphological agglomeration definition and is based on the following official and academic sources (all accessed/updated 2024–2025):

1. Eurostat – Geographic Units: Functional Urban Areas (2024 edition)
   Official database of all European FUAs with population and commuting data.
   ec.europa.eu/eurostat → Cities and Greater Cities
2. United Nations – World Urbanization Prospects: The 2024 Revision
   Primary source for urban agglomerations outside the EU (Russia, Ukraine, Turkey, Balkans, etc.) and for cross-checking continuous built-up area delimitations.
   population.un.org/wup
3. OECD – Redefining “Urban”: A New Way to Measure Metropolitan Areas (2022–2025 update)
   Harmonised methodology applied to all OECD countries (including Poland, Czechia, Germany, Netherlands) – especially important for correctly capturing polycentric regions such as Rhein-Ruhr, Upper Silesia and Randstad.
   oecd.org → Redefining Urban

Where national statistical offices (GUS Poland, Destatis Germany, INE Spain, etc.) provided newer or more detailed 2023–2025 estimates, those figures were used to fine-tune the final numbers.