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I wanted to find the volume of water in an olympic-size swimming pool. In one source I got the value of 660,253.09 gallons of water. Knowing that there are at least two values of a gallon, roughly 3.8 liters and 4.5 liters, I looked up the names and values of these two types of gallons. The approximate 4.5 liter gallon is known as the imperial gallon, and the approximate 3.8 liter gallon is known as the US gallon, or more specifically the US liquid gallon.

In the Wikipedia article on the gallon the first photo in the introduction shows a can of gasoline which is said is for use in the US and Canada, and is labeled in imperial gallons. (Error: It shows "imperial gallons" for Canada and "US gallons" for the USA.

Further down in the article it shows a photo of an American fuel pump, with prices shown in what I think are US liquid gallons.

So it appears that both imperial and US liquid gallons are used in the US.

My question is, how can I know which type of gallon unit is used when reading about gallons, for example, with the information about the swimming pool?

Zebrafish
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  • If you read the comment under the first photo you cited, it clearly says the marking in imperial gallons is "for Canadian use", not "for U.S. use." But the article you cite deals with numbers very poorly: from measurements such as "approximately $50$ meters" it computes a volume to eight digits of alleged precision. If someone were to build a pool to exactly those dimensions (no extra room for the touch pads), what about the fillets where the wall meets the bottom? Don't use such an author as a source of numerical data. – David K Oct 05 '19 at 18:28
  • If you look up "Olympic-size swimming pool" on Wikipedia instead of "gallon," you'll get the volume in liters, U.S. gallons, and imperial gallons (without the absurd extra digits of precision). – David K Oct 05 '19 at 18:30
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    Just to be clear, imperial gallons are not customarily used in the U.S. – David K Oct 05 '19 at 18:31
  • @DavidK I'm sorry, I missed that, it clearly says imperial gallons for Canada and US gallon for US on the can. So in other words, though Wikipedia says both imperial and US fluid gallons are used in the USA, I should assume that in the USA gallons means US fluid gallons, as that's the one in predominant use. – Zebrafish Oct 06 '19 at 07:30

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