When you see “8 oz.” on a recipe, you probably accept it without thinking. Yet the abbreviation “oz” seems oddly disconnected from the word ounce. Why that strange “z”? The answer lies in linguistic history, medieval trade, and centuries of adaptation.
In this article you’ll learn how “oz” evolved, why it stuck, how the ounce itself came to be, and how different “ounces” still exist in modern measurement.
The Ancient Roots: Latin “Uncia” and the Roman System
The story begins with Latin. The Roman Empire used a unit called “uncia”, meaning “one-twelfth.” In the Roman system, a pound (libra) was divided into 12 uncia. Over time, uncia became the root not only for our ounce, but also for the inch (a twelfth of a foot).
In Latin, “uncia” referred to a twelfth part of a libra pondo (a pound by weight). As Roman influence spread, uncia morphed in local languages. In Old English, the word became ynce, which later evolved into “inch.” Simultaneously, the idea of a twelfth unit also influenced weight vocabulary.
Through Old French and Anglo-Norman, uncia became once, unce, then ounce in English. That transformation preserved the sense of a small portion of a larger whole.
From Onza to “Oz” in Italian and Medieval Trade
While English speakers called the measure “ounce,” Italian and Spanish speakers used onza or onza (or oncia in later Italian). It is from this Italian/Spanish form onza that the z emerged. In medieval Italy, merchants and scribes abbreviated onza as oz, planting the “z” that English eventually inherited.
By the 1540s, English texts began using oz. as the standard abbreviation for ounce—borrowing that Italian contraction even though English spelling lacked a “z.” The abbreviation “oz.” thus reflects a cross-linguistic borrowing, preserving the Italian form in written shorthand.
Why Not “onc” or “oun”?
You might wonder: since “ounce” in English doesn’t include a “z,” why didn’t the abbreviation become “onc” or “oun”? The reason is that abbreviations were not always formed from the English spelling. Medieval scribes and scholars often borrowed abbreviations from Latin or Romance languages. So even though English spelled the word without a “z,” the abbreviation came from Italian onza, keeping the “z” intact.
Moreover, medieval manuscripts frequently used contraction marks—elongated tails, superscripts, or loops—to indicate missing letters. The “z” in manuscripts was often stylized, making “oz” a convenient and well-recognized shorthand among educated readers.
How the Ounce Has Shifted Over Time
The ounce is not a single fixed unit historically. Several “ounces” exist:
- Avoirdupois ounce – the common ounce used in the US, equal to 28.349523125 grams. Sixteen of these make a pound.
- Troy ounce – used for precious metals, equal to 31.1034768 grams. Twelve troy ounces make a troy pound.
- Apothecary ounce – an older unit used in pharmacy, essentially equivalent to the troy ounce (often represented by the ℥ symbol).
Though the systems differ, all these ounces share the same “oz” abbreviation — often with a qualifier (e.g. “oz t” for troy).
The U.S. & Avoirdupois: Why We Still Use “Oz”
In the United States, the avoirdupois system remains standard for everyday goods. Under that system, one pound equals 16 ounces. The international yard and pound agreement of 1959 fixed the avoirdupois ounce precisely at 28.349523125 grams. Because oz was already well established, there was no incentive to change it.
Americans still see ounces in food labels, postal weight, body weight in some contexts, and in casual recipes. The enduring abbreviation “oz” has become so ingrained that changing it would cause confusion.
Why the “Dot”? Why “oz.” vs “oz”?
Traditionally, abbreviations in English came with a period (or full stop), so oz. was common. Over time, usage has shifted and many modern styles drop the period, simply writing oz. Some formats (like nutritional labels) omit the dot to save space or standardize style.
How “Oz” Survived When Other Abbreviations Changed
English is full of odd abbreviations. For example, “pound” is abbreviated lb (from Latin libra), and “ounce” uses oz, from Italian onza. Because many measurement abbreviations derive from Latin or Romance languages, they often keep foreign letters or odd spellings. Over centuries, “oz” survived because it was short, unambiguous, and widely understood.
Practical Examples & Modern Use
- In recipes: “2 oz cheese” means two avoirdupois ounces unless otherwise noted.
- In precious metals: “1 oz t gold” means one troy ounce.
- On product labels: nutrition facts might list “oz (g)” to show both ounces and grams.
- In printing: fabric weight may be listed in ounces per yard squared.
Common Questions About “Oz”
Is “ozs” acceptable for plural? Usually not. The form oz is used for both singular and plural. You’ll rarely see “ozs.”
Does “oz” only mean weight, or can it mean volume? Sometimes “fl oz” stands for fluid ounce, a volume measure. In that case, we use fl oz to differentiate from mass.
Is “oz” international? In metric countries, ounces are mostly obsolete, but you may still see oz in imported goods or specialty contexts.
Why the Abbreviation Doesn’t Match English Spelling
The abbreviation doesn’t match the English spelling because it came through Italian, not English. The spelling “ounce” reflects the English phonetic evolution of French/Latin root unca, uncia. But the abbreviation mirrored the Italian form—oz from onza—and stuck.
Lessons from This Strange Abbreviation
- History drives abbreviations. What seems illogical now often made sense in the Middle Ages.
- Cross-language influence is powerful. English borrowed not just words but abbreviations from Latin, French, and Italian.
- Practical use cements odd forms. Once “oz” became widespread, consistency forced it to stay.
- Abbreviations can outlive original forms. Even though English no longer uses “onz…” forms, oz persists.
Conclusion
Ounce traces back to Latin uncia, meaning a twelfth part of a Roman pound. Over centuries that became Anglo-French ounce in English. But the abbreviation “oz” came through medieval Italian onza, preserving the “z” that English spelling lacked.
The use of oz dates back many centuries and entered English usage by the 1500s. Through trade, printing conventions, and standardization, oz became the immediate shorthand for any ounce—avoirdupois, troy, or apothecary.
Even today, Americans recognize oz from nutrition labels to recipes. The odd mismatch between “ounce” and “oz” makes sense only when seen through the lens of linguistic history and the twists of medieval transcription.