Imperial Units of Measurement

Podcast Transcript

Almost every country in the world uses the metric system…..almost.

There are still a few stragglers, like the United States, who use units handed down to them from the British. These are known as Imperial Units.

These units often confuse those living in countries that use the metric system….as well as those who live in countries that use Imperial Units.

They don’t often make sense. They don’t have any consistency between units, and their histories are quite murky.

Learn more about imperial units and how they were developed on this episode of Everything Everywhere Daily.

Even if you use imperial units on a daily basis, if you take a step back, you can appreciate the absurdity of it all.

The whole point of the metric system is that everything is done on the basis of base-10. There are consistent naming conventions, and regardless of whether you are dealing with length, weight, or volume, you know that smaller and larger units will involve multiplying or dividing by some multiple of ten.

Imperial units, on the other hand, are all over the place. Units might be a half, a third, a fourth, an eighth, a twelfth, or more based on other units measuring the same thing.

Moreover, there are some antiquated units that are almost never used anymore except in a few niche circumstances, which only add to the confusion.

So, let’s start this discussion by talking about units of length. I’ll begin with the smallest unit most people use, the inch.

The inch gets its name from the Latin unit known as the uncia. Through several changes in language and pronunciation, uncia became inch and it is also the basis of the word ounce. Uncia simply means 1/12 in Latin.

In other countries, the word for inch is derived from the word for thumb. If you remember back my origin of words and phrases episode, the “rule of thumb” is that the width of a thumb is approximately one inch.

The Roman uncia was one-twelfth of the Roman foot, which was the base unit of length.

While all Imperial Units come from the British, the British origins mostly come from the Romans.

After the Norman invasion of England in 1066, the inch was defined as being three barleycorn. While a barleycorn was defined as a third of an inch, literal barleycorns were used to measure it. In the law known as the Composition of Yards and Perches, which was enacted in 1266, it defined an inch as “3 barly cornes dry and rounde.”

There are antiquated units that were smaller than a barleycorn. A line was a quarter barleycorn or one-twelfth of an inch.

A digit was ¾ of an inch, and a finger was ? of an inch.

You can see the reason why all of these were created. They used common objects or body parts for measurement. You can also probably see the problem with these units: they weren’t standard.

A nail, which was a unit of cloth measurement, was three digits or two and a quarter inches.

A palm was three inches, and a hand was four inches. For some odd reason, hands are still used today to measure horses, even though it would be just as easy to use feet or inches. Horses are measured from the ground to the base of the neck.

A shaftment was defined as the width of an outstretched thumb with the fingers together. It was initially defined as six and a half inches, and later, it was simplified to six inches.

An American one-dollar bill is 6.14 inches, so almost one shaftment.

A span is the distance from the tip of your thumb to the tip of your little finger. In ancient cultures, this was defined as one-half a cubit.

Twelve inches is, of course, one foot. There were two basic units that ancient cultures used for length. The cubit, which is defined as the distance from the tip of your middle finger to your elbow, and the foot, which was the length of a human foot.

India, Egypt, and Mesopotamia all used the cubit, whereas Rome, Greece, and China used the foot.

The Roman foot was defined by Marcus Agrippa, the best number two guy in history if you remember back to my episode on him, as literally the length of his foot.

The Roman foot eventually fell into disuse after the collapse of the western empire, but the idea of a foot stuck around.

Three feet constitutes a yard, which is still a common unit of measurement. An American football field is 100 yards.

Two yards or six feet is a fathom. Originally, a fathom was defined as the distance from the tips of the fingers when an adult male had his arms outstretched.

Fathoms are still used to measure water depth, and the British Navy defined a fathom as one-thousandth of a nautical mile, which is 6.08 feet.

A rod is the next largest unit, and it has had many different definitions over time. It was eventually set as 16 1?2 feet or 5+1?2 yards. That seems odd, but it also works out to 1?320 of a mile.

The rod was a unit traditionally used by surveyors. One of the benefits of using a rod was that it was easy to define an acre with it. One acre is 160 square rods.

A rod was also known as a perch or a pole.

A chain is four rods or 66 feet or 22 yards. You don’t hear about the chain unit of measurement very much, but it was actually very important at one time because it was the primary unit of measure for surveyors.

The name comes from a surveyor’s chain, which was used to conduct surveys.

A link is defined as one-hundredth of a chain.

A furlong is 40 rods, ten chains, or 660 feet or more, usually defined as one-eighth of a mile. The word furlong comes from the length of a furrow on one acre of land. It was generally considered the length that an ox could plow a field without resting.

An acre is defined as one furlong long and one chain wide.

Today, the only place you’ll find furlongs being used is in horse racing.

Finally, we get to the mile. The mile is currently defined as 5,280 feet, 1,760 yards, 320 rods, 80 chains, or eight furlongs. To be technical, this is known as a statute mile.

The word mile comes from the Roman word for thousand. A Roman mile was 1000 strides, also defined as 5000 Roman feet.

By the time of Queen Elizabeth I, there were different distances for the mile floating around. This was due to an earlier redefinition of a foot. Five thousand feet didn’t add up to 320 rods anymore.

The decision was made to keep with the shorter foot, which is how we got 5,280 feet. This decision was made primarily for tax reasons, as by changing the units, there were now more acres of land to tax.

One of the most confusing things about the mile is that there are two different units called the mile. The statute mile, which I just mentioned, and the nautical mile.

In many ways, the nautical mile is much simpler and cleaner than the statute mile. A nautical mile was defined as one minute of arc along a line of longitude on Earth.

This makes a nautical mile longer than a statute mile, but not by much. The idea of using the curvature of the Earth was a good one, but the problem is that the Earth isn’t a perfect sphere.

Near the equator, a nautical mile is 6,046 feet, and near the poles, it is 6,107.5 feet.

The British Navy defined a nautical mile as 6,080 feet, and the Americans defined it as 6,080.2 feet.

The current internationally accepted definition is that a nautical mile is 1,852 meters or 6,076.11548556 feet.

The final unit of length is the league. A league is defined as three miles. On land, it is a statute mile, and at sea, it is a nautical mile.

I covered length first because area and volume are, for the most part, based on the square or cube of units of length.

The most common units of area in Imperial units are square feet or square yards, which is pretty self-explanatory.

The one unit that requires some explaining is the acre. An acre was originally defined not just as an area but as a set of particular dimensions. It was a plot of land that was one chain or four rods wide by one furlong long.

Eventually, it just became a unit of area that was 1?640 of a square mile, or 4,840 square yards, or 43,560 square feet. Nice, round, easy-to-remember numbers.

Volume units are odd just because the tradition developed of different products having different units.

The standard fluid volume units start with the minim. Traditionally, the minim was measured as a single drop. Technically, today, it is defined as 0.06 mL.

Sixty minims constitute a dram, and 80 minims make a teaspoon. A tablespoon is equal to 4 drams, or 240 minim, or three teaspoons.

A fluid ounce is two tablespoons.

Five fluid ounces is one gil, a unit only used in measuring alcohol nowadays. However, it is only five ounces in the UK.

The United States has a system of United States customary units which deviates slightly from the British units. In the US, 1 gill is four fluid ounces.

Four gils make a pint. The difference in the number of ounces in a gil is the reason why the British and American pints are different sizes. If you go to a pub, a British pint glass will be 20% larger than an American equivalent.

Two pints make a quart, two quarts make a pottle, and two pottles make a gallon.

To add to the confusion, wine and beer have separate measurements. They are all based on the size of kegs and barrels that are used. Just to make things confusing, a wine gallon is measured differently from a regular gallon, both British and American.

A wine barrel is 31.5 gallons, and a beer barrel is 35 gallons.

Two barrels are a hogshead, two hogsheads are a butt, two butts are a tun. Tun is spelled “t-u-n” and is not the same as the unit of weight.

Also, if someone ever says that they have a butt load of something, it would technically have to be a lot of beer or wine.

Finally, we can turn our attention to weight and mass, which is also super confusing because there are three different systems: Avoirdupois, Troy, and Apothecary.

Troy units are only used for precious metals, and the Apothecary system was used in medicine. Both troy and apothecary units are very similar. However, apothecary units are not really in use anywhere anymore, as the medical profession in both the US and the UK now uses the metric system.

If you get a drug, it would be measured in grams or milligrams now.

The weights you might be familiar with are called avoirdupois.

The smallest unit is the grain. Traditionally, the grain was defined as the weight of a single grain of barley from the middle of the ear. The grain is used in all three systems, and its weight is the same in all three.

From the grain, you next have the dram, which is confusing because it is also a unit of volume. The modern definition of a dram is that it equals 27 and 11?32 grains. Again, nice, easy round numbers.

Sixteen drams make an ounce, which is again confusing because there are also fluid ounces, a measure of volume.

Sixteen ounces make a pound.

In the UK, and pretty much nowhere else, human weight is measured in stone. One stone equals fourteen pounds.

A hundredweight is equal to eight stone or 112 pounds in the UK and 100 pounds in the US.

Finally, the British ton, or the long ton, is 20 hundredweight or 2240 pounds. The American ton, or short ton, is just an even 2000 pounds, but still 20 hundredweight.

Just to add one final bit of confusion to everything, there is a metric tonne, which is usually spelled t-o-n-n-e which is equal to 1000 kilograms or one meaggram. It is slightly less than a long ton and slightly more than a short ton.

I’ll end the episode by touching on the temperature unit, Fahrenheit.

The odd thing about Fahrenheit is that the zero point is totally arbitrary. It is the temperature at which a solution of water, ice, and ammonium chloride happens to freeze. Why that mixture? Good question.

Because they used that mixture, you wind up with water freezing at an awkward number, 32 degrees.

The reason why the boiling point of water was selected at 212 is because it is 180 degrees from freezing. Daniel Gabriel Fahrenheit the creator of the system selected “degree” as the unit, which, also confusingly, is the same name as the units for measuring angles.

Because the two opposite points on a circle are 180 degrees apart, he put the freezing and boiling points of water 180 degrees apart from each other.

If everything I’ve covered in this episode seems confusing….it is, and this is exactly why the metric system was developed. Most people who even use some of these units aren’t entirely sure how many of them makeup one of something else.

Prior to the metric system all of this was ever worse because every country or region would often have their own units of measurement.

All of these units of measurement actually made sense at one point when we didn’t have or need very accurate systems of measurement. The length or weight of a grain of barley or the width of a finger was fine for most purposes 500 years ago, but they could never work in a modern world with precise measurements.

That is why almost everyone in the world has moved on from these antiquated units.