4 ms·

No but seriously, what is a gallon?

• ColinWright 7y ago
  So obviously you've read the Wikipedia article[0], so beyond that, what are you actually asking? [0] https://en.wikipedia.org/wiki/Gallon https://en.wikipedia.org/wiki/Gallon
  • michaelt 7y ago
    When a car in the UK lists fuel consumption in miles per gallon, are they using US or imperial gallons?
    • pacaro 7y ago
      Imperial gallons, I would wager that most British people aren't aware that the US gallon is different.
      • RandallBrown 7y ago
        What kind of car is it? If it was an American car, I might expect it's US gallons.
        • pacaro 7y ago
          My data in the UK is nearly 20 years out of date, but historically most American car manufacturers that sold cars in the UK made market specific models. Ford is a great example of this. Even if you sell the same model, you are already making significant changes for the driver side being mirrored... I think the difference in the gallon size has often been used, wittingly or otherwise, to exaggerate the poor gas mileage of American vehicles (the "yank tank" trope in British culture)
      • billpg 7y ago
        But the US Gallon is currently in everyday use. The Imperial Gallon hasn't been used for decades, having long since been replaced by the litre for fuel purchases.
        • pacaro 7y ago
          But the US gallon has never been used in the UK, and there is a temporal continuity of usage in mpg, people like to compare across time, a discontinuity would be weird
    • bryanlarsen 7y ago
      If a salesmen is telling you a mpg number it's imperial gallons because then the number is smaller and it sounds better.
• Koshkin 7y ago
  Looks like different liquids can have different sizes of gallon. (Interestingly, the US "standard" gallon is the same as wine gallon.)
• deleted 7y ago
  [deleted]
• sverige 7y ago
  I learned this when I was about five years old: A cup is 8 ounces. Two cups in a pint, two pints in a quart, four quarts in a gallon. In other words, 128 ounces. This is of course for U.S. gallons. A lot of things now measured in the metric system are still based on the standard U.S. system, just converted to metric. This is, for example, why whisky comes in 750 ml bottles instead of (say) one liter bottles. It was traditionally sold in fifths (of gallons); i.e., 25.6 ounces, which converts to 757.1 ml. It's also why there are track events of 100 meters, 200m, 400m, 800m, and 1600m. They are near the distance of the old races, and it seems especially noticeable to me for the half mile and mile, probably because I ran those races when I was a teenager. Thankfully there's almost zero chance the U.S. will convert to metric in my lifetime. I can feel miles and gallons and Fahrenheit in my bones. Metric, not so much.
  • dreamcompiler 7y ago
    Or if you're a binary geek like me, 1 gallon = 2^7 ounces.
  • buckminster 7y ago
    The standard running race is 1500m, which doesn't make any kind of sense.
• tialaramex 7y ago
  Well conveniently the one thing everybody agreed on is that it's some amount of litres. They don't agree how many, but they did all give up on trying to define it any other way than via SI units like the litre (the US gallon is defined in cubic inches, but its inch is defined in metres so that gets you back to litres). The even better news is that the litre is defined in terms which you can use for yourself from first principles. So you can thus find out what a gallon is! First build a Caesium atomic clock, it will need to be cooled to as close to 0K as you can get. This will allow you to determine a second. Now, in a vacuum, or as close to one as you can get, measure how far light travels in this second. This will enable you to determine a metre, you can use this metre to determine a litre of volume and then apply the definition of a gallon. All previous standards for the gallon relied on prototypes, a government owned "the gallon" or "the inch" and you could only have a copy, at best. But the litre is something you can just determine for yourself the same way you could work out Pi. Unlike a prototype "gallon" or "inch" Caesium atoms are found all over the universe and you can make your own (Kids: Do not try to make your own Caesium at home) and light is readily available or can be made too. Like estimating Pi, the more effort you put in, the closer to exact your approximation will be. Unfortunately even a poor approximation of the litre is harder to achieve than a one digit approximation of Pi, but it isn't impossible.
• shirro 7y ago
  It is an accessibility layer for SI units. When I go into a bar in Australia and order a beer it is whatever the locals call it. A pot, a schooner, a pint. In most states a pint is 570ml which is about a 20 fl oz UK pint. Except in one where it is a bit less than a 16 fl oz US pint at 425ml so you have to ask for a real pint. It doesn't really matter because beer isn't traded across borders in pints. For science and commerce you can't afford the confusion over all these local units. But for ordering beer it doesn't matter. No issue with US sports using customary units. I use them all the time for height and sports in a country that has been metric for decades. But when science commentators or NASA use them I cringe hard.