Imperial VS US gallon

[leehljp]

I didn't know this:

"The gallon in the UK is an Imperial gallon which equals 4,546 liters. The US gallon equals 3.785 liters. In other words, an Imperial gallon equals approximately 1.2 US gallons. A more accurate measurement would be, 10 US gallons equal 8.33 Imperial gallons. 40 mpg in the States would equal 48 mpg in the UK."

Metric vs imperial causes enough problems, now I just learned that Imperial (UK) and US gallons are not the same.

The above quite came from a guy answering another on the Rav4 Hybrid forum who was upset that UK Rav4's were getting about 10 more MPG than the US ones.

[LCHIEN]

Here's another... long Ton (UK Ton), Short Ton (US Ton), Tonne (Metric Ton) (a 1000 kg or a Megagram), All somewhat close (less than 12% difference) but different so very confusing.

I made this chart to help me identify them to each other and to pounds and kg.

[LCHIEN]

Most people think for some reason that the US uses Imperial units. I really hate when people ask why does the US use Imperial units. US units preceded Imperial by more than 50 years.

The US uses a system called US customary system or USCS for short. This is an adoption of the old English units which were used by the English and adopted by the US colonies; some of the English units came from as far back as the Roman; the US units were used throughout the US colonies and thus were the units of the fledgling US country well before 1776.

Imperial Units were a major change for England; by royal degree they were implemented in 1824, nearly 50 years after the US departed from English rule, so the decree had no effect on the US, although used widely in other colonies. England joined the Metric world in 1965, I think, ending Imperial. Except for road speeds and pub drink volumes.

Metric was developed by the French; revolutionary France had, it was alleged about 1 million different units among the provinces and total confusion. So it was commissioned and designed and implemented in 1798, some time after the USCS (which was in Use as I said well before 1776).

Imperial has for linear measures feet, inches yards, miles which were taken directly from the old English units and therefore the same as USCS inches feet miles etc.
However the units for volume (Pints, gallons) and weight were all changed; the Imperial gallon comes from the volume of water that weighs 10 pounds (sort of taking after the kg which is the mass of a liter of water) so its off by about 20% from US Gallons. Units for weight also changed.

It should also be noted that the English used several different gallons depending on what was being measured. The Gallon that the US copied from the old English was the Queen Anne's gallon, used for wine most often.

The confusion over USCS vs Imperial comes because of the common length units.
It also is confused by tool makers who label their Tools like wrenches and sockets METRIC and IMPERIAL. While its sort of correct that inch dimensioned fasteners are Imperial, they are USCS. And the other thing is that people confuse fractional inch measurements as being Imperial.
The standardization of fractions inch fasteners (i.e. 3/16, 1/4, 5/16, 3/8 inch etc ) fasteners is because the SAE (the US society of Automotive Engineers) long ago standardized US fastener sizes (shanks, hex head size across the flats, thread pitches) in binary fractional increments rather than decimal fractions.
Some tool makers label the tool sets METRIC and SAE which is probably more correct. The Brits have their own fastener sizes called Whitworth which can be analogous to SAE. Metric fasteners are really a standardized set of metric values, like SAE, I call the M-series, usually whole or half mm shank, head and pitch sizes for fasteners... Commonly called Mxx where xx is the mm size of the fasteners head.

So the point of this is for education, and to ask you to please stop referring to USCS units and SAE standard fastener sizes as Imperial!!!

[leehljp]

"The US uses a system called US customary system or USCS for short." - I did not know that. My 2nd and third grade teacher (early '50s) held to British standards in measurements, and that confused me in the 4th - 6th grade to when I finally made a subconscious transition to a normal/standard US numbers.

"It also is confused by tool makers who label their Tools like wrenches and sockets METRIC and IMPERIAL." THAT is where my confusion comes from today!

THANK YOU LORING! That helps explaIn a lot!

[LCHIEN]

Another oddity is that "customary system" is not capitalized for some reason I can't recall.
Imperial and USCS are quite different, despite what CHATGPT says.

[Nick Keenan]

Ever wonder why a mile is 5,280 feet? Until about the year 1100 a mile was 4800 feet, 1600 yards, 8 furlongs. A chain was 20 yards and a rod was 5 yards. There were 80 chains in a mile and 320 rods in a mile. An acre was ten square chains, or a furlong by a chain, or a rod by a quarter mile. All very logical.

The problem was there were two competing standards for feet, the long foot and the short foot. England used the long foot, and the rest of Europe used the short foot. By 1100 there was enough international trade that the difference was a problem, and England switched from the long foot to the short foot. This created a different problem. In 1066 William the Conqueror had invaded England, and one of the first things he did was to survey the entire country so that he could tax it effectively. That survey is known as the Domesday Book. When England switched over to the short foot they didn't want to have to redo the entire survey, it had been a huge undertaking. Instead they only changed the foot and the yard, and then redefined all of the other measures used for surveying so that their size didn't change.

The old long foot was equal to 1.1 short feet. So it was still three feet to the yard, but now the rod became 5.5 short yards, the chain 22 short yards, the furlong 220 short yards and the mile 1760 short yards, or 5280 short feet.

If you work only in surveying units it's still logical, there are still 8 furlongs in a mile, 80 chains and 320 rods. An acre is still ten square chains or a chain by a furlong. It's only if you mix in feet and yards that it gets complicated.