The imperial system is a funny thing. Like, really funny. So funny that there is actually a unit of measurement for wine (or whiskey) casks called a "butt." That means if you fill the barrel up, you technically have a buttload of wine—though you'd probably just call it a full butt. Are you laughing yet?
Okay, seriously, though. Not a lot of people still talk in terms of tuns and butts any more. The antiquated terms are likely only used at wineries and distilleries these days, but they're still fascinating, if only because the etymology offers a trip back in history when big barrels of alcohol brought nations together. The words are not only derived from Old English but also Dutch, Italian, and French. Butt actually comes from "botte," a Medieval French and Italian word for boot. In Italy, at least, botte is still used to refer to a wine cask.
At this point you're probably wondering just how much wine it takes to make a buttload. The actual amounts have varied somewhat ever the years, but we'll go with the numbers provided by the Macallan distillery in Scotland. According to those folks, a butt is 108 Imperial gallons*. It is also half a tun which is 216 gallons. A third of a tun, 72 gallons, is a puncheon, and a third of that is a tierce. Half of a butt, 54 gallons, is called a hogshead. A boring old barrel is just 36 gallons, and a LOL-worthy kilderkin is 18 gallons. The smallest unit is nine gallons, and it's call a firkin, because of course it is. You can also call it a rundlet.
Keep in mind that these words are used in a measurement system that was basically invented by cave men. The Imperial system measures the weight of humans in stones and the height of horses in hands. And good luck trying to remember how to convert things, because there is absolutely no rhyme or reason to the formulas. The words are fun, though!
* - Imperial gallons are equivalent to about 1.2 American gallons.