29 July 2014

People of Britain

As a follow up to the previous post, if an olympic swimming pool has under a million gallons of water, rather than the billion gallons claimed by Glasgow 2014, what does have a volume of 1 billion gallons?

Well, obviously an olympic-size swimming pool of depth 3–4 km deep would have that volume, but you don’t see too many of those around.

Also, the volume of the Great Pyramid of Giza is apparently around 2.5 million cubic metres, which is about 550 million gallons, and as far as I can tell both the John Hancock Tower and the Burj Khalifa have volumes of around 330 million cubic metres so other possibilities are:

  • 2 Great Pyramids of Giza
  • 3 John Hancock Towers
  • 3 Burj Khalifas.

But a more interesting answer is suggested by Wolfram Alpha. It suggests “1% of all humans alive on the planet Earth” (which I suspect is very similar to “1% of all humans alive”). This is a fantastic answer, especially since the population of the world is about 7 billion and the population of the UK is roughly 1% of that (some 63 million in 2012). (Wolfram alpha defaults to US gallons, but that’s a only a factor of 0.8, and in fact if you switch to imperial gallons the the 1% just switches from being a slight underestimate to slight overestimate.) So perhaps the best answer I can come up with is

  • all the people in Britain.

We can sense check that, and it seems to work. 1 billion divided by 70 million is about 14, so if a person is about 14 gallons, this is right. And since a gallon is about 4.5 litres, this is about 63 litres, and since people are mostly water and have a rather similar density to water, this corresponds to an average weight of about 63kg. This is at least in the right ballpack, and perhaps quite close, since the BBC reports the ONS as saying that the average British man weighs 83kg and the average woman 70kg. Allowing for some children, 63 sounds about right.

In fact, since people are 70% water, a billion gallons of water isn’t even that far off the amount of water in all the people of Britain. Fantastic!