Ever since I was a little kid learning the units of liquid measure, I’ve been a bit bothered by a couple of gaps in the progression.  I mean, everyone knows a pint is two cups and a quart is two pints, but then out of nowhere a gallon is four quarts.  I think some good portion of the population probably remembers the song “I Love You a Bushel and a Peck” and knows that a peck is two gallons and a bushel is four pecks (and a barrel is four bushels – but I don’t know how a heap is defined).  Then if you know beer, you probably know that a keg is two bushels, and a barrel is two kegs.  Also, on the smaller end of things, an ounce is two tablespoons but then a cup is eight ounces, and eight is the third power of two, so it seems like there are a couple of missing units there too.  So why the breaks in this otherwise-binary progression from tablespoon to barrel?

Well, the other day I got around to investigating this old pet peeve, and I found out that my elementary school curriculum was sadly lacking.  In fact there is a word for two quarts (or a half gallon), and that word is pottle.  So now I no longer go to the store for a half-gallon of milk; instead I procure a pottle of milk.

Likewise there is no naked jump from peck to bushel; in between lies the kenning, with a volume of four gallons or two pecks.  In fact, there’s an extended binary progression extending below cups and above barrels!  Here’s what I’ve pieced together from various sources:

a minim is basically about a drop (except that a minim is a defined quantity, whereas a drop varies in volume);
a fluid drachm is 60 minims;
a tablespoon is 4 fluid drachms;
(a tablespoon is 3 teaspoons;)
a fluid ounce is 2 tablespoons or 8 fluid drachms; (but there are 16 drams in an ounce-force [which is a bit confusing since dram sounds like drachm]);
(a jigger is 3 tablespoons [so there’s a sort of trinary progression from teaspoons to tablespoons to jiggers];)
a double-shot (or tot) is 2 fluid ounces;
a gill is 2 tots; (pronounced “jill”)
(a wineglass or lowball is 3 double-shots;)
a cup is 2 gills;
(a highball is 3 gills;)
a pint is 2 cups;
a quart is 2 pints;
a pottle is 2 quarts;
a gallon is 2 pottles;
a peck is 2 gallons;
a kenning is 2 pecks;
a firkin or a bushel is 2 kennings;
a rundlet or a keg or a kilderkin is 2 firkins or bushels;
a barrel is 2 rundlets or kegs or kilderkins;
(a hogshead is somewhere around 1.5 to 2 barrels;)
a tierce is 2 barrels; a puncheon is also approximately 2 barrels;
(a butt is typically about 3 barrels;)
a vat is 2 tierce; a pipe is approximately 2 puncheons or hogsheads;
a tun is 2 pipes (and, interestingly, also weighs about a ton);
and a cauldron or chaldron is 4 vats or about 2 tuns.

… and here’s a nice table of conversions:

There’s a lot of very interesting history behind these measures. For example, as a beer brewer, I know that a keg is actually 15.5 gallons and a barrel is 31 gallons. This probably has something to do with beverage merchants historically shortchanging their customers – or possibly when the measures were set out legally, it was deemed desirable that anything over 15.5 gallons should satisfy a contract to deliver a “keg,” thereby allowing for such things as evaporation and minor spillage.

If you’re a fan of Alton Brown’s cooking show Good Eats (as I am), then you’ve heard the rhyme, “a pint’s a pound the world around.” I would add, “and a ton’s a tun, or most of one.” Of course, these rhymes only apply to water, upon which Earth’s gravity acts with approximately one ounce-force per ounce-volume… depending on how hot the water is among other factors. The rhyme also, apparently, does not apply in the UK, where an “Imperial pint” is 20 ounces, which is a pound-and-a-quarter, because an Imperial gallon is defined as 10 pounds.