Recently, my wife and I picked up a new trailer, which has a 28 gallon black water tank for … well, you know. Holding black water.
But we weren’t sure if it was actually 28 gallons, so we went to great pains to measure out how much liquid it could actually hold.
Not by, you know, using it until full, but by filling up a water container (7 gallons) and dumping it into the toilet.
First issue. Was the holding tank US gallons or Imperial Gallons? Fortunately, it provided the measurement in kilograms, which allowed us to calculate the amount in litres (because 1 kg of water is equal to 1 litre of water, and vice versa), and it turned out that yes, the tank was US Gallons. How about the blue water container? Also US Gallons. Yay.
But the fact that there are two different gallons? Boo. Boo to the max.
The trouble is, of course, that there are two different systems of measurement. We talk about the Imperial system, but quite often, we use the US customary system of measurements.
These measurements are reworkings of a system of measurements that was cobbled together from the measurements used by the Romans fused together in an unholy alliance of disparate measuring systems.
Take, well, the gallon as a for instance. It was originally used to measure beer and wine. Or rather, they were used to measure, as the volume of wine in a gallon of wine was different than the volume of wine in a gallon of beer.
The wine gallon weighed in (or rather, volumed in) at 3.7854 litres or so, and dates from the 13th century, when the Tractus de Ponderibus et Mensuris laid out the volume of a gallon: ““Twelve Ounces make a Pound and Eight Pounds make a Gallon of Wine; and Eight Gallons of Wine make a Bushel of London; which is the Eighth Part of a Quarter.”
Of course, what this means is anyone’s guess, but probably wound up being about 224 cubic inches.
(The Tractus also contains such brilliant bits as “A Sack of Wool ought to weigh Twenty-eight Stone, that is Three hundred and fifty Pounds, and in some parts Thirty Stone, that is Three hundred and seventy-five Pounds, and they are the same according to the greater or lesser Pound. (“greater or lesser Pound”. R. D. Connor has identified the lesser pound with the silver-mark pound of Bruges, 14 ounces each of 480 grains = 6720 grains, and the heavier with the short-lived English wool pound of (16 tower ounces of 450 grains) 7200 grains. 350 x 7200 = 375 x 6720.)
Are you with me so far? Because we’re not there yet.
The gallon grew from 224 cubic inches in the 16th century, then shrunk to 231 by the 17th.
Because the English were trading wine through the Flemish city of Bruges, the standard of weights used was Parisian. Water weighing 8 livre of Paris occupied a volume of about 224 cubic inches. The livre was divided into 15 ounces, each weighing about 30.6 grams. (Side note: this is why the British Pound symbol is an L: Livre, or Libra, meant pound, and a one pound note was the equivalent of 1 pound of silver.)
The volume of wine in a gallon was finally settled on in 1706 as 231 cubic inches.
This meant that when the US declared independence in the late 1700, the wine gallon was just laying around, waiting to be used.
Meanwhile the British, having both a wine gallon and an ale gallon to choose from, decided to use the ale gallon, which was—by this time, 277.4194 cubic inches, down from the original 282. (Why was the ale gallon different than the wine gallon? I only have half a page here, so let’s just say “because;” and leave it at that.)
The Imperial measurement system came into effect in 1824, about 30 years after the Americans set in place their system of measurements, and so diverges from the US system in a number of places.
All this is to say that to know what a gallon is, you have to know whether it’s a US gallon or an Imperial Gallon. You also need to know if it’s a dry measure or a wet measure, because for some unknown reason, the US decided it would be a good idea to divide it up even further. So a dry gallon is about 155 imperial fluid ounces, but a wet gallon is 133 imperial fluid ounces.
Sigh.
All this is just preamble to an important milestone that recently came about.
The US has finally decided on which foot to use.
Because of course, they’ve been using two types of foot measurements for the last 50 years or so.
You see, there is a US Survey Foot and an International Foot.
The length of the US Survey Foot was first outlined in the Metric Law of 1866 and specified that one meter is equal to 39.37 inches. Shortly thereafter, the United States defined the yard as equal to 3600/3937 meters. With some additional math you arrive at the relationship that one US Survey Foot is equal to 1200/3937 meters or .3048006096.
In 1957, the International Yard and Pound Agreement set the length of the international yard to be .9144 meters.
This means that an international foot is shorter than the US Survey foot. Not by much, but by 2 ppm.
Most of the land in the US was surveyed using US Survey feet. But since the mid-1900s, some states have adopted the International standard while others haven’t. That means that if you bought an acre of land in California (which uses US survey feet), it would be 160 sq. cm bigger than in either Oregon or Arizona, which both border the state, and both use the International Standard.
That is, until 2023, when all states will finally adopt the International standard.
Of course, it might have been easier to have just adopted the metric system (upon which both other systems are based), but for now, let’s celebrate the small victories.
