A Bit on the History of The British Imperial System of Weights and Measures

weights-and-measures.jpg In 1965, the British Imperial System of Weights and Measures was replaced by the metric system, used in Europe since the days of Napoleon in the 19th Century. The change has been a gradual one for the UK, and, today, most weights, lengths, and volumes are measured and labelled metrically. The United States Customary System of weights and measures is derived from the British Imperial System.

According to the Encyclopedia Britannica, “The British Imperial System evolved from the thousands of Roman, Celtic, Anglo-Saxon, and customary local units employed in the Middle Ages. Traditional names such as pound, foot, and gallon were widely used, but the values so designated varied with time, place, trade, product specifications, and dozens of other requirements. Early royal standards established to enforce uniformity took the name Winchester, after the ancient capital of Britain, where the 10th-century Saxon king Edgar the Peaceable kept a royal bushel measure and quite possibly others. Fourteenth-century statutes recorded a yard (perhaps based originally on a rod or stick) of 3 feet, each foot containing 12 inches each inch equaling the length of three barleycorns (employed merely as a learning device since the actual standard was the space between two marks on a yard bar). Units of capacity and weight were also specified. In the late 15th century, King Henry VII reaffirmed the customary Winchester standards for capacity and length and distributed royal standards (physical embodiments of the approved units) throughout the realm. This process was repeated about a century later in the reign of Queen Elizabeth I. In the 16th century the rod (5.5 yards, or 16.5 feet) was defined (once again as a learning device and not as a standard) as the length of the left feet of 16 men lined up heel to toe as they emerged from church. By the 17th century usage and statute had established the acre, rod, and furlong at their present values (4,840 square yards, 16.5 feet, and 660 feet, respectively), together with other historic units. The several trade pounds in common use were reduced to just two: the troy pound, primarily for precious metals, and the pound avoirdupois, for other goods sold by weight.”

fabric-measurements-guide-by-buyandcreate.png Ironically, the British still use “pint” and “mile” as they once were considered, but most other weights and measurements have been changed to metric. The British Imperial System was based on the human form. I recall so easily when my mother was measuring fabric and determining a yard how she would hold the one end of the fabric between her finger and thumb and stretch out her arm to her side. She would bring the other end of the fabric to her nose after she turned her face in the opposing direction of her stretched out arm. That was her “yard.” The 5th Century philosopher Protagoras reportedly said, “Man is the measure of all things.” Many took this statement quite literally. 

The basic unit of length for the English was the yard, which was originally set as the distance between Henry I’s nose and the tip of his outstretched arm. I Never Knew That About London by Christopher Winn tells us, ” In the 14th century many items in the markets in and around St Paul’s were sold by the ‘St Paul’s foot,’ a measurement based on the length of the foot of St Algar, carved on the base of one of the columns near the cathedral entrance. This soon became a standard measurement and was the origin of one ‘foot’ (12 inches or 30.48 cm).” When the Romans occupied England, they brought with them the concept of 1000 paces equalling a mile. A pace was FIVE Roman feet. A Roman mile, therefore, became 5000 paces. It was Elizabeth I who changed the mile to 5280 feet (or eight furlongs). 

The furlong was based on the length of a long furrow in a plowed field. A rod was based on the accepted length of the ox goad or prod used by medieval farmers. An acre was set as one furlong by one rod. An agreement of the national standard of weights and measures can be found as far back as the Magna Carta. But it was during the reign of George IV that the Weights and Measures Act came into effect. This act, along with the another in 1878, established the British Imperial System. This system was based on precise “understandings” of existing units of measure. “The 1824 act sanctioned a single imperial gallon to replace the wine, ale, and corn (wheat) gallons then in general use. The new gallon was defined as equal in volume to 10 pounds avoirdupois of distilled water weighed at 62 °F with the barometer at 30 inches, or 277.274 cubic inches (later corrected to 277.421 cubic inches). The two new basic standard units were the imperial standard yard and the troy pound, which was later restricted to weighing drugs, precious metals, and jewels. A 1963 act abolished such archaic measures as the rod and chaldron (a measure of coal equal to 36 bushels) and redefined the standard yard and pound as 0.9144 metres and 0.45359237 kg respectively. The gallon now equals the space occupied by 10 pounds of distilled water of density 0.998859 gram per millilitre weighed in air of density 0.001217 gram per millilitre against weights of density 8.136 grams per millilitre.


The former Weights and Measures office in Seven Sisters, London (590 Seven Sisters Road). https://en.wikipedia.org/wiki/Imperial_units#/media/File:Weights_and_Measures_office.jpg

“While the British were reforming their weights and measures in the 19th century, the Americans were just adopting units based on those discarded by the act of 1824. The standard U.S. gallon is based on the Queen Anne wine gallon of 231 cubic inches and is about 17 percent smaller than the British imperial gallon. The U.S. bushel of 2,150.42 cubic inches, derived from the Winchester bushel abandoned in Britain, is approximately 3 percent smaller than the British imperial bushel. In the British system, units of dry and liquid capacity are the same, while in the United States they differ; the liquid and dry pint in Britain both equal 0.568 cubic decimetre, while the U.S. liquid pint is 0.473 cubic decimetre, and the U.S. dry pint is 0.551 cubic decimetre. British and American units of linear measure and weight are essentially the same. Notable exceptions are the British stone of 14 pounds, which is not used in the United States, and a divergence in definition of the hundredweight (100 pounds in the United States, 112 in Britain) that yields two different tons, the short U.S. ton of 2,000 pounds and the long British ton of 2,240 pounds. In 1959 major English-speaking nations adopted common metric definitions of the inch (2.54 cm), the yard (0.9144 metres), and the pound (0.4536 kg).” (British Imperial System)

In another Christopher Winn book, I Never Knew That About the English (Ebury Press, ©2008, pages 115-116), Mr. Winn tells us, “Weights were even more complicated, but were based on multiples of a grain of barley, except when it came to money, and then it was a grain of wheat. Money was based on weight and hence 240 pennies, which made up one pound in weight, became one pound in money terms as well…. Some old units have quietly died away. A guinea was one pound, one shilling, and was widely used as a conventional method of payment in auctions or transactions where a percentage was to be paid to a third party…. A league was three miles, the distance a man could comfortably walk in one hour.”

From Encyclopedia Britannica

unit abbreviation
or symbol
equivalents in other units
of same system
Avoirdupois1 avdp    
short ton   20 short hundredweight, or 2,000 pounds 0.907 metric ton
long ton   20 long hundredweight, or 2,240 pounds 1.016 metric tons
hundredweight cwt    
short hundredweight   100 pounds, or 0.05 short ton 45.359 kilograms
long hundredweight   112 pounds, or 0.05 long ton 50.802 kilograms
pound lb, lb avdp, or # 16 ounces, or 7,000 grains 0.454 kilogram
ounce oz, or oz avdp 16 drams, 437.5 grains, or 0.0625 pound 28.350 grams
dram dr, or dr avdp 27.344 grains, or 0.0625 ounce 1.772 grams
grain gr 0.037 dram, or 0.002286 ounce 0.0648 gram
stone st 0.14 short hundredweight, or 14 pounds 6.35 kilograms
pound lb t 12 ounces, 240 pennyweight, or 5,760 grains 0.373 kilogram
ounce oz t 20 pennyweight, 480 grains, or 0.083 pound 31.103 grams
pennyweight dwt, or pwt 24 grains, or 0.05 ounce 1.555 grams
grain gr 0.042 pennyweight, or 0.002083 ounce 0.0648 gram
pound lb ap 12 ounces, or 5,760 grains 0.373 kilogram
ounce oz ap 8 drams, 480 grains, or 0.083 pound 31.103 grams
dram dr ap 3 scruples, or 60 grains 3.888 grams
scruple s ap 20 grains, or 0.333 dram 1.296 grams
grain gr 0.05 scruple, 0.002083 ounce, or 0.0166 dram 0.0648 gram




About reginajeffers

Regina Jeffers is the award-winning author of Austenesque, Regency and contemporary novels.
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