I mean, since:
2 cups = 1 pint
2 pints = 1 quart
2 quarts = 1 ???
2 ??? = 1 gallon.
Given the pattern, surely there was a standardized unit that belongs in the ??? position.
(If not, let’s invent one.)
Quarts are called quarts because they’re a quarter of a gallon, so I don’t think there was ever a named two-quart unit.
But you forgot that a cup is two gills.
They’re not necessarily regular. A firkin (of beer) is 9 gallons, and a barrel is 36 gallons (usually).
2 quarts = a half gallon. That works well enough that another word isn’t needed.
There are no such regularities in the Imperial system. The pattern you think you have seen there is a spurious one, largely the result of your use of the cup as a unit, which really belongs to separate, less formal system that just happens to coordinate with the (American variant of) the Imperial system for capacity. The proper subdivision of the pint is the gill, of which there are four to a pint.
Imperial measures of most types are even less regularly arranged than those for capacity:
[ul]
[li]12 inches to the foot.[/li][li]3 feet to the yard[/li][li]22 yards to the chain[/li][li]10 chains to the furlong[/li][li]8 furlongs to the mile[/li][li]3 miles to the league[/li][/ul]
(and that is not bothering with rods, poles, or perches)
[ul]
[li]16 ounces to the pound[/li][li]14 pounds to the stone (Americans don’t use stones much, but it is still so)[/li][li]8 stone to the (imperial, or long) hundredweight[/li][li]twenty hundredweight to the ton[/li][/ul]
(and that is just avoirdupois, leaving aside Troy weight).
In that case, the forty is the beer unit between the quart and the gallon.
I think at the 7-11 they call that a “Medium”. 
Let’s call it the ha’gallon. Aren’t there some hogsheads and jeroboams in there to account for as well?
This is where the growler should fit in.
A pottle.
:dubious: Well, but there ought to be. What was wrong with you all??
I could get behind ha’gallon, but it should have an even more shortened pronunciation due to laziness over the years. So maybe it could be a ‘hagal’, promounced like haggle.
Oooh, ooh! A winner! And a nice word, not confused with any other meaning. And I think poets would appreciated rhyming it with “bottle.”. 
If we’re going to do that, let’s call it the chuck.
Came in here to contribute pottle, but someone beat me to it.
There’s about half a dozen different units called a barrel. It usually depends on what you’re measuring and sometimes which country you’re measuring it in. Oil barrels are 42 US gallons, for example.
Right. The table should read like this:
4 fluidrams = 1 tablespoon
2 tablespoons = 1 fluid ounce
4 fluid ounces = 1 gill
2 gills = 1 cup
2 cups = 1 pint
2 pints = 1 quart
2 quarts = 1 pottle
2 pottles = 1 gallon
So there’s actually two holes in the system. There’s no unit equal to 2 fluidrams and none equal to 2 fluid ounces.
Note: these are only in the US Customary system. As njtt notes, the Imperial system does not have the nice base 2 hierachy in the smaller units. Their pint is 20 fluid ounces, and it’s a slightly different sized fluid ounce. This is the result of Britain “reforming” their system back in the 1820s where they made the gallon be the volume of 10 pounds of water rather than 8[sup]1[/sup] as was previously used. The US did not go along with this abomination so we still use the correct gallon.
I’ve ignored some units that don’t fit the base 2 hierarchy, such as the teaspoon ( = 1/3 tablespoon).
[sup]1[/sup] The definition of the US gallon is 231 cubic inches, which is actually about 8 1/3 pounds of water, although this will vary depending on temperature.
What really irks me is that ounces are units of both volume and weight. That, basically, is why I prefer metric. That, and I really like engineering notation.
What is “wrong” (if anything is) is that Americans are too lazy, jingoistic, and hidebound to switch to metric.
Well done!!! You had this one!! For some reason the conversation just kept rolling along, but this splendid play should be well noted.
I read somewhere that pottle fell from use when printed material became widely available due to proofreaders changing it to bottle.
Moderator Note
Let’s keep jabs against a particular nationality out of General Questions. (Given that you are well aware that you are insulting a large number of board members, this kind of remark could also be viewed as trolling.) No warning issued, but don’t do this again.
Colibri
General Questions Moderator
It works well; it’s what I’ve always called the unit in practice (e.g. a half-gallon of milk); and it’s analogous to our coinage (4 quarters = 1 dollar, 2 half-dollars = 1 dollar).
For the past decade at least, I’ve used fractions or multiples of the femtoliter for liquid measure. You are welcome to join me.