The humble pound and ounce are so embedded in Britain‘s language, culture and collective memory, it‘s easy to forget they were once at the center of a centuries-long battle to standardize the nation‘s weights and measures. The Imperial system we know today is the product of a fascinating history stretching back to antiquity, shaped by ancient civilizations, medieval power struggles, and the demands of modern global trade. Let‘s unpack the twisting, contentious tale of how pounds and ounces came to be.
From Libra to Pound: Ancient Origins
Like many Imperial units, the pound and ounce have Roman roots. The Roman libra was a unit of mass equivalent to about 328.9 grams, or 12 uncia units. The Latin uncia became the English ounce, while libra gave rise to the abbreviation "lb" for pound.
Interestingly, the Romans had their own system of subunits, shown in the table below. Many were based on the mass of different numbers of wheat grains or carob seeds. The siliqua, for instance, was 1/1728 of a libra, and equivalent to about 0.19 grams – the weight of a single carob seed.
| Roman Subdivisions of the Libra | Modern Equivalent (grams) |
|---|---|
| Siliqua | 0.19 |
| Scrupulum | 1.137 |
| Sextula | 4.55 |
| Uncia | 27.3 |
The uncia, or ounce, was 1/12 of a libra. Though the Romans also had a different pound, the libra mercatoria, for trade, the libra system of 12 unciae to a pound forms the basis of the troy weight system used for precious metals to this day.
Over time, the Roman units were adopted and adapted by other European cultures, including the Anglo-Saxons in England. The tower pound, based on the weight of 5400 grains of barley, was one such variation in wide use in Britain by the medieval period.
The Magna Carta and Medieval Measurement
Reliable, standardized weights and measures became increasingly vital as trade and taxation expanded in the Middle Ages. Merchants and monarchs alike had a vested interest in establishing agreed-upon units. This struggle came to a head in 1215 when English barons forced King John to sign the Magna Carta, a charter of rights that included a section on weights and measures:
"There shall be standard measures of wine, ale, and corn (the London quarter), throughout the kingdom. There shall also be a standard width of dyed cloth, russet, and haberject, namely two ells within the selvedges. Weights are to be standardised similarly."
This was among the first attempts to legislate standard measures across England. But it would still be centuries before pounds and ounces were reliably the same from shire to shire. In 1588, Queen Elizabeth I ordered the creation of a "Standards of Weights and Measures" but these remained more guidelines than firm definitions.
The Imperial System Takes Shape
In the 19th century, Britain was at the height of its power, with a global empire upon which "the sun never set." With such far-reaching dominions, the need for a coherent, standardized system of weights and measures became acute. Parliament passed the Weights and Measures Act in 1824 to establish the Imperial system across Britain and its colonies.
This Act set down precise definitions for units like the pound, gallon and foot that would be used uniformly throughout the Empire. The Imperial pound (or avoirdupois pound) was defined as the mass of a platinum cylinder kept by the Exchequer, equal to 7000 troy grains (about 453.59 grams).
The 1824 Act was refined and expanded with further legislation like the Weights and Measures Act of 1878. The 1878 Act, for instance, tweaked the definition of the Imperial pound to 0.45359237 kilograms, a standard that persists to this day.
Resisting the Metric Tide
Even as the Imperial system crystallized in the 1800s, it faced stiff competition from the metric system that had emerged after the French Revolution. Metric units, based in multiples of ten and natural constants like the circumference of the Earth, were enthusiastically taken up by much of the scientific community as well as nations across continental Europe and Latin America.
But Britain, perhaps wary of a system born of the overthrow of a monarchy, stuck stubbornly to its Imperial units throughout the 19th and early 20th centuries. They became tightly bound up with British identity even as the Empire unraveled in the postwar period.
In the 1970s, the UK‘s entry into the European Common Market led Parliament to officially begin metrication, passing laws to phase out Imperial units. This sparked an outcry among traditionalists, and some pushback. The so-called "Metric Martyrs," a group of market traders convicted in the early 2000s of selling produce in pounds and ounces, became a cause célèbre for those who saw Imperial measures as a bastion of British culture against European encroachment.
Today, Imperial units are officially a thing of the past in the UK, with a few exceptions. Draught beer and cider are still sold by the pint in pubs, road signs are in miles per hour, and height is often discussed in feet and inches. The troy system of pounds and ounces also lives on for precious metals. A troy pound is heavier than a standard pound, equaling 5760 grains or about 373.24 grams.
Across the pond, customary units used in the United States remain closely aligned with the old Imperial system, one of the reasons the US is one of just three nations worldwide not to have fully adopted metric measures. Myanmar and Liberia are the others.
An Enduring Legacy
The winding path of pounds and ounces over the centuries illustrates how deeply woven into culture and identity our systems of measurement can become. Though officially replaced by metric units in the late 20th century, many Britons still cling to Imperial measures out of tradition, nostalgia or nationalist sentiment.
Undoubtedly, the metric system offers enormous advantages in terms of logical coherence, mathematical ease, and international harmonization. But the long, storied history of Imperial units like the pound and ounce testifies to how even something as ostensibly neutral as a unit of mass can be bound up with the currents of politics, commerce and cultural change that shape a society over time.
