Product labels in American grocery stores are cluttered with incoherently rambling scrawls of mixed measurement units all because the federal government is too incapacitated to allow metric-only labeling. Passing a proposed amendment to the U.S. Fair Packaging and Labeling Act (FPLA) is all it would take to bring Americans one step closer to sanity, but the Food Marketing Institute is blocking this amendment.
Walk up to any American and ask (without being too rude) what the difference is between an ounce and a fluid ounce. Then ask about a troy ounce and whether the British also use ounces. More than likely you will either get a blank stare or the wrong answer. If you have not yet been punched in the face, and if you are brave enough to amuse yourself even more, ask which units we use to measure mass and volume. If you are an American, do not feel too bad if you struggle with such a seemingly simple line of inquiry. It is not entirely your fault; the American educational system utterly fails to teach students how to measure in the Modern Era.
Our English word ounce derives from Latin uncia, a unit that was one-twelfth of the Roman pound (libra). We incorporated this word into Old English as ynsan or yndsan from an unattested Vulgar Latin form and then into Middle English through Anglo-Norman and Middle French (unce, once, ounce). The abbreviation oz came later from the cognate Italian word onza (now spelled oncia).
Our English word inch comes from the same Latin word, but we gave it an i-mutation as we incorporated the word into Old English.
The obsolete apothecaries’ ounce is equivalent to the troy ounce. Maria Theresa ounce found its way into Ethiopia and some European countries and was equal to the weight of one Maria Theresa thaler, or 28.0668 grams. Both the weight and the value are the definition of one birr, still in use in present-day Ethiopia. By the way, the thaler was a silver coin used throughout Europe for almost four hundred years. The name thaler lives on in the many currencies called dollar.
People in England used the now obsolete Tower ounce of 450 grains in English mints, the principal one being in the Tower of London. The Tower ounce dates back to the Anglo-Saxon coinage weight standard, but Henry VIII in 1527 abolished it in favor of the Troy ounce.
The Yankees, Brits and former territories of the long-gone British Empire defined the avoirdupois ounce as exactly 28.349 523 125 g under the yard and pound agreement of 1959. In the avoirdupois system, sixteen ounces make up an avoirdupois pound, and the avoirdupois pound is defined as 7000 grains; one avoirdupois ounce is therefore equal to 437.5 grains. Laughably, the ounce is actually still a standard unit in the United States, while the English now mainly use the ounce informally. Nostalgically clinging to long-gone days of glory, some in England still use ounces in restaurants to describe steak or burger portion sizes even though it ceases to be a legal unit of measure in Britain way back in the year 2000.
A troy ounce is equal to 480 grains. Consequently, the international troy ounce is equal to exactly 31.103 476 8 grams. There are 12 troy ounces in the now obsolete troy pound.
Today, the troy ounce is used only to express the mass of precious metals such as gold, platinum, palladium, rhodium or silver. Bullion coins are the most common products produced and marketed in troy ounces, but precious metal bars also exist in gram and kilogram sizes. A kilogram bullion bar contains 32.150 746 569 troy ounces.
A fluid ounce is a unit of volume (also called capacity) a tiny percentage of humanity still typically uses for measuring liquids. People have created various definitions throughout history, but only two have survived the scrap heap of history: the British Imperial fluid ounce and the United States fluid ounce.
An imperial fluid ounce is 28.413 062 5 mL or 1⁄20 of an imperial pint or 1⁄160 of an imperial gallon.
A US fluid ounce is 29.573 529 562 5 mL or 1⁄16 of a US fluid pint and 1⁄128 of a US liquid gallon, making it about 4% larger than the imperial fluid ounce.
Instead of clinging to outdated legacy units of measure, Americans would do well to at least understand how things are measured on Earth. These charts show the vast superiority of the International System of units:
What natural standard would one use if one were to design a measurement system from scratch? Does every person on Earth identify with some common natural standard? What do all humans have in common? How is Nature a standard?
People share Earth as a common home. We use Earth Circumference as a linear standard. What better standard is there for Earthlings? Earth measures ten million meters from equator to pole. Earth is actually the standard we use for the length of the meter. Did you know that? Primates share the common characteristic of having ten fingers. People all around our Metric Planet use a base-ten number system simply because it is part of our anatomy. Multiplying and dividing by factors of ten is the fundamental International System scheme.
Volume is simply a matter of using a linear measure for three dimensions. A liter is a cubic decimeter. So we have a natural linear standard and a natural standard for volume, but what about mass? A liter of air is much less dense than a liter of gold for example because different substances have different densities. What natural standard can we use for mass / weight? This question leads us to another standard we find in Nature:
We all depend on water to sustain our lives, so we use the density of common water as a natural standard. A liter of water weighs one thousand grams, which is one kilogram. We measure things small and large in modern times with the International System (SI). We are no longer limited to those old quaint limited-range obsolete units of measure.
SI allows us to measure vastly smaller things like subatomic particles and DNA strands and vastly larger things like planetary orbits and intergalactic distances. It is only natural that people create appropriate units for appropriate uses. General consensus among archaeologists is that human life has its origins in the East African Rift Valley two million years ago. All humanoids ultimately emerged from a branch of primates from Africa. We are all descendants of our Paleolithic ancestors, ultimately quite African, having migrated prehistorically in successive waves to nearly every patch of habitable space on Earth. Humans have come a long way since we migrated out of Africa. No human is a foreigner when you consider Earth your home, so let us all use the same measurement system that is based on Earth and Water.