About nine million. That is the answer most people want, and it is close enough for most purposes.
But if you need the number to be right rather than close, there isn't one. There are several, they differ by millions, and they are all correct.
The four answers
| What you mean by "London" | Population | Source |
|---|---|---|
| The City of London (the square mile) | 15,111 | ONS mid-2024 |
| The London place, roughly the urban core | 8,961,989 | GeoNames |
| Greater London, the 33 boroughs | 9,089,736 | ONS mid-2024 |
| The Greater London built-up area | 9,787,426 | ONS, 2011 census |
The spread between the smallest and largest of those is about 9.77 million people. That is not a rounding difference or a data quality problem. Each figure measures a different thing, and each is right about the thing it measures.
Why the built-up area is bigger than Greater London
Greater London is an administrative boundary drawn in 1965. The built-up area is a physical one: ONS defines it from Ordnance Survey topographic data as land that is irreversibly urban, where buildings are generally less than 200 metres apart.
London's bricks do not stop at the boundary. The built-up area spills into Hertfordshire, Essex, Kent, Surrey, Buckinghamshire and Berkshire, which is why it counts more people than the 33 boroughs do. Anyone who has watched the houses fail to thin out on the train to Watford already knows this.
The City of London is the strange one
Only 15,111 people live in the City of London, the historic square mile that is legally a city in its own right. Roughly half a million commute in to work there. It is the only local authority in Britain where the daytime population is more than thirty times the resident one.
So when a list says London's population is around fifteen thousand, it is not broken. It is answering a question you did not ask.
ONS finds this awkward too
This is not us being pedantic. When ONS published its built-up areas analysis for the 2021 census, it had to handle London separately: the method does not identify individual settlements there the way it does elsewhere, so London is reported by borough, and its 33 built-up areas were removed from the main analysis altogether.
When the national statistics office takes your capital city out of its own dataset because the geography will not behave, the problem is real.
What it looked like in 2005
The World Gazetteer, which this domain published until 2013 and whose 2005 edition we have restored, handled it by publishing both figures and labelling them. London appeared as 7,421,209 as a place and 12,599,561 as an agglomeration. Two numbers, both stated, twenty years ago.
Most population lists still do not do this. They pick one figure, print it without saying which geography it describes, and that is precisely why no two of them agree.
So which number should you use?
Whichever matches your question, as long as you say which one it is.
- Comparing cities internationally? Use the built-up area or the metropolitan area, and use the same basis for every city in the comparison.
- Writing about policy, funding or local government? Use Greater London, because that is the unit that has a mayor and a budget.
- Quoting a single number in passing? Say "about nine million" and nobody will mind.
The one thing worth avoiding is picking a figure because it is the one you found first. See the current UK population tables, where we state the geography for every figure, and the annual series for each London borough.