How many journeys are made on the London Underground each day?

How to get close to this number

Work from the city population. Greater London holds around nine million people, and on a working day a substantial minority make one or two Tube journeys. A third of the population making two trips gives roughly the right figure — and journeys, not people, is what is being counted.

The comparison with Tokyo on this site is the instructive one: a tenth of the volume for a city a quarter of the size. Ridership scales with density and with how much of a metropolitan area the network reaches, not with population alone, and this system covers a far lower share of its region's trips than the Tokyo one does.

The air conditioning detail in the explanation is a genuine engineering consequence of the age. The deep tunnels were bored before anyone anticipated cooling, and they are too tight to fit the equipment or to vent the waste heat — so the oldest underground railway in the world is also the hardest one to cool. Being first has costs that last a century and a half.