Why isn't a gallon the same size in the U.S. and UK?

[Charlie_Tan]

Inches are inches, feet are feet.
But a U.S. gallon is 3.785 liters and a UK gallon is 4.546 liters.
Why the discrepancy?

[something_clever]

holy crap… i didnt feel like reading this whole thing but it answers your question somewhere in all that

[something_clever]

I would quote the exact text but I don’t know how to do that properly and not get the moderators angry at me for plagarism or something weird like that, so specifically scroll down to “Volume by Volume”

[Ice_Wolf]

According to this page, the divergence came in 1824 when the UK adopted the Imperial measure, while the US standardised a wine measure used previously.

At one time, the British gallon differed depending on what you were measuring, and where you were measuring it. But, by the 19th century, two definitions had survived: the Queen Anne (or Wine) gallon, which was 231 cubic inches, and the Winchester (or Ale) gallon, of 282 cu in.

In 1824, the British abandoned both the Ale and the Wine gallons in favour of the Imperial gallon, based on the volume of 10 pounds of water (which works out at 277.41945 cu in). America, by this time, had already standardised on the Wine Gallon of 231 cubic inches (strictly speaking, this was defined as the volume of a cylinder 6 inches long and 7 inches in diameter, or 230.9070 cubic inches).

[Earl_Snake-Hips_Tucker]

This has already been answered, but here’s an earlier thread with some good information (assuming the links inside still work):

http://boards.straightdope.com/sdmb/showthread.php?threadid=8953

[Charlie_Tan]

Thanks guys. Let this thread sink to oblivion.

tG

[Dogface]

And feet and inches also not identical. According to a “Documenta Geigy” I have that’s about 30 years old, until 1960, the US inch (and all US linear measures) was slightly larger than the Imperial inch (and all Imperial linear measures). This difference was roughly 0.0003cm, if I can remember correctly.

Then the USA redefined the inch to equal exactly 2.54cm (it had equalled something like 2.540001cm or something like that, according to the measurements of the day).