How we predict today's tube temperature
Why "predicted," not "measured"
There's no public live feed of tube temperatures - TfL doesn't publish one. What we publish instead is a modelled estimate: our best calculation of what each line's platforms are likely to feel like today, based on the weather and over a decade of TfL's own published temperature history. We're upfront that it's an estimate, and we show a likely range rather than a single false-precise number, because that's the honest way to present a prediction.
What goes into the estimate
Three things, in plain terms:
Today's weather. We start with today's forecast for London. Some lines - particularly the sub-surface ones like the District and Circle - sit close to street level and respond almost immediately to however hot or cold it is outside.
How the last few weeks have gone. The deep tube lines don't cool down overnight. Tunnels dug metres into London clay absorb heat gradually over weeks, and release it just as slowly - which is why the Central or Bakerloo line can still feel stifling several days after a heatwave has broken. We account for this by factoring in the recent run of weather, not just today's number, so the lines that "remember" heat are modelled as remembering it.
Each line's own character. Every line on the network has its own personality when it comes to heat - a mix of how deep it runs, how it was ventilated when it was built, how much has been upgraded since, and how frequently trains run. Some lines run consistently warmer than others even in the depths of winter; some barely notice a heatwave; some have been getting hotter year on year quite apart from the weather. We've studied over a decade of TfL's own published line-by-line temperature data to capture these individual differences, so each line's prediction reflects its own real-world behaviour rather than a single network-wide assumption.
Putting it together
We combine those three factors into a single estimate for each line, refreshed several times a day as the day's actual weather becomes clearer - an early read in the morning, and updates around midday and again ahead of the evening commute. Each prediction comes with a likely range rather than one number, because a model is a best estimate, not a thermometer.
Why the sub-surface lines are one number, not four
The District, Circle, Hammersmith & City and Metropolitan lines share platforms, tunnels and, for long stretches, track - so TfL itself publishes their temperature data as a single combined figure rather than measuring each line separately. We report it the same way TfL does: one number for "sub-surface lines," covering all four. It's not a choice we made to simplify things; it's the level of detail that exists in the data we start from. In practice this is a reasonable grouping anyway - these four lines are all shallow, cut-and-cover construction, quite different from the deep-level lines, and behave far more similarly to each other than to, say, the Northern or Victoria line.
Platform temperature isn't carriage temperature
One important distinction: everything on this site is a platform prediction, not a carriage one - and the two can differ quite a bit, in opposite directions depending on the line.
On lines without air conditioning - currently Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria and Waterloo & City - a packed carriage can feel noticeably hotter than the platform itself. Body heat from a full rush-hour train adds up in an enclosed space with limited airflow, so treat our platform estimate as a floor, not a ceiling, on how the carriage will actually feel at peak times. (The Piccadilly line is mid-transition to new air-conditioned trains during 2026, so this will improve there over time - we'll update this page as the rollout progresses.)
On the sub-surface lines - Circle, District, Hammersmith & City and Metropolitan - trains are air-conditioned, so the carriage will typically feel noticeably cooler than the platform prediction, even on a hot day.
In short: our number describes the platform you're standing on while you wait, not the carriage you'll be sitting or standing in - factor in your line's air-conditioning status accordingly.
What this isn't
This isn't a live sensor reading, and it isn't a substitute for TfL's own service updates or safety guidance during extreme heat. On unusually severe or fast-moving weather days, treat our number as a strong steer rather than gospel, and always follow TfL's official advice if it's a genuinely hot day on the network.
The data behind it
The model is built on over a decade of TfL's own published Underground temperature data, cross-referenced against London weather records from the Met Office. The way we combine them into a daily prediction - the model itself - is our own work and is proprietary; see our Terms of Use (/terms) for details. We're always looking to make the estimate sharper, including through requests for more detailed data directly from TfL.
Get in touch
If a prediction looks off, you've got feedback, or you're interested in API access beyond normal personal use (see /terms), email tubetemp@outlook.com - we read everything, and heatwave season is exactly when we're paying closest attention.