Whilst on the topic perhaps you might to look up the derivation of the gallon and the US gallon!
In days of yore the traders who imported wines and spirits were forever complaining about short measure when the ship docked. Added to which HM Customs & Excise levied import duties on such items and this caused even more dissent to the traders. In a famous trial in the High Court in London a trader was hauled before the court because it was alleged he had understated the quantity of wine which he had imported and was due to pay duty on. This was regarded as a very serious offense and could mean execution if found guilty!
However, this trader was not as dumb as they thought. He had ascertained that in fact there was no official definition of the gallon and HM Customs & Excises did not have a certified measure which could define what a gallon actually was. So the judge let him off and this caused a lot of red faces in the government.
Enter Queen Anne, the last of the Stuart family who rose to the throne in 1702. It seems her husband, who was a Danish prince, was interested in weights and measures and such like and his country had gone through a similar fiasco a little time before, so he was well aware of the problem. Her Majesty ordered the government to do something about it and bl**dy quick at that or heads would roll.
So the brightest (maybe not) minds set to with great determination to define the English Gallon measurement. After much faffing about it was agreed that an English Gallon would be that amount of "Good Thames Water" (River Thames water, which was an open sewer at the time, so it must have been a bit smelly) that would fill a circular container measuring exactly 7-inches in diameter and exactly 6-inches in height. And so came into being in 1707 what became known as the "Queen Ann English Wine Gallon" and laws were passed in Parliament and by Royal proclamation that this was now the official gallon measure and calibrated cylinders were made and assized and kept in the Tower of London for reference. Along with this it meant that all the wooden casks, barrels and other larger and smaller containers had to have a definite volume assigned to them, so everybody was singing off the same hymn sheet. And the Customs and Excise men were very pleased and levied duties on all and sundry.
Now the interesting bit.
Around the same time the Americans decided to standardise on a gallon, as they had just had a big punch up with the British which they won and declared Independence from the Crown, they thought that as they also imported wine and other spirits in wooden casks and barrels they would adopt the same measures, as it meant the politicians didn't have to trouble their heads with such worries.
It came to pass that the Queen Anne Wine Gallon was a bit off and all the other wine casks, barrels etc needed to be adjusted to get everything into line. But the Americans seemed not to be aware of this fact and went on their merry way using the obsolete Gallon measurement.
Fast forward a few years and in the early 1800s oil was discovered in Pennsylvania. The oil well drillers needed a suitable container to put the oil into for transportation and having looked around found lots of wooden casks and barrels no longer needed as the wine etc had been drunk. They chose a wine barrel as the best option as it could be lifted and moved easily and it held 42 of their obsolete US gallons – which at the time was actually now 36 English or Imperial Gallons, today it is 35 Imperial Gallons.
The largest wooden container used for wines etc was the Tun, it held 216 Queen Anne Wine Gallons. Half this volume was a Butt and it held 108 English Gallons at the time. A Puncheon was 1/3 rd of a Tun and held 72 English Gallons. Going down in size we have the Hogshead, Tierce, Barrel, Kilderkin, (an adopted Dutch measure), Firkin, Pin, and these contained 54, 42, 36, 18, 9 and 4 1/2 English Gallons. So the sizes were logical and normally decreased by a factor of 2. The odd one out is the Hogshead, there were two the Wine Hogshead and the Ale Hogshead.
What the Americans called a Barrel is in fact a Tierce, which is French for 1/3 and a Tierce is half a Puncheon, which is 36 English Gallons in measure. And it seems the Americans for some reason got the Tierce and Barrel confused, so that is why today we have a barrel of crude oil as being 42 US Gallons! In Metric measures it is as near as makes no difference 159 litres.
Edited By John Fielding on 25/02/2016 17:20:55