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Is the US fluid ounce the same volume as the Imperial fluid ounce?
The US fluid ounce is the same as the Imperial one - the amount of water that weighs an ounce. There are 20 fluid ounces to an Imperial pint, but only 16 in US; there are eight pints in a gallon in both systems, but since the size of the pint is different, the size of the gallon is therefore different. I do not know why the decisions were made, but the 16 fluid ounces in the US pint of water weigh one pound; whereas, as every English schoolboy used to know before we were infiltrated by the evil French system, in the Empire a pound of water weighed a pound and a quarter.
Asked on 15 December 2010 by DS, Houston, Texas
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Many thanks. Another reader referred me to the Wikipedia entry that shows the derivation to be the measure for a gallon of wine v/s the measure for a gallon of ale (which presumably accounts for expansion). We use the ale measure. The Yanks use the wine measure.
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fluids
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