In the U.S., the standard unit of land measurement is the “acre,” which is exactly 4,840 square yards, or 43,560 square feet. The history of how we settled on this seemingly random area and why we are one of the few industrialized countries still using it is a lot more interesting than you might think.
Measuring land for ownership is an ancient concept and most systems of measurement were based on then-current farming practices. In the Anglo-Saxon world, oxen were most commonly used to plow fields and pull carts. The very first specifications of an acre were meant to represent the typical area of land that could be plowed in one day with one farmer and a yoke of oxen. A “yoke” is a wooden beam used between a pair of oxen and attached to the plow they are pulling.
One of the oldest explicit references to an acre as a unit of land measurement comes from an English statutory legal text from the 13th century that defines one acre as a unit of land “40 perches in length and 4 in breadth.” Also called rod or pole, “perch” derives from an ancient Roman form of measurement that represents the combined length of 20 average human feet. For its use in defining the acre, it meant as much as a team of oxen could plow in a day. The length of the acre (the furrow-long, or furlong) is as far as the team can plow without needing a break. The breadth (width) was the number of furrows that could be plowed before the oxen had to be put out to pasture for the day.
Obviously, this was not at all a precise or reliable way to calculate anything, so authorities eventually began standardizing the area. Britain’s King Henry VIII during the 16th century was the first to introduce standardized units of land measurement. Two early tools were designed to measure land – the rod and the chain. Both were also used interchangeably as units of measurements.
The rod as a unit of measurement is exactly equal to the perch, which was standardized at 16.5 feet. The rod tool consisted of a stiff iron bar wrapped with a wax-coated cord that was knotted at regular intervals. One square rod is the square measure of a tract of land 1 rod by 1 rod and is equal to 272.5 sq. ft. Additionally, 40 square rods are defined as 1 “rood” and there are 160 square rods (4 roods) to a 1 acre.
The chain unit was based on the lengths of the chains in what is known as a “Gunter’s chain,” which was used to survey not only the British Empire, but also early American settlements. Designed and introduced in 1620 by English clergyman and mathematician Edmund Gunter, the 66-foot chain is divided into 100 links, usually marked off into groups of 10 by brass rings or tags. Each link is about 7.92 inches. Since an acre measured 10 square chains in Gunter’s system, the entire process of land area measurement could be computed using measurements in chains, and then converted to acres by dividing the results by 10. By 1675, the chain had become the common unit of measurement of length, along with the furlong. Link chains were later superseded by the steel ribbon tape, an early form of the tape measure.
Our modern-day specifications of an acre are part of the United States customary system of measurement units that was formalized in 1832. The United States customary system (USCS or USC) developed from English units known as the “imperial system” which were in use in the British Empire before the U.S. became an independent country. In the late 20th century, Britain and most other industrialized countries began adopting the metric system so today, agricultural land in most of the world is measured in hectares, which is 10,000 square meters. Today, the acre is used in a number of current and former British Commonwealth countries by custom only.
The U.S. has made moves to adopt the metric system several times but our USCS system has prevailed. The biggest reasons the U.S. hasn’t adopted the metric system are time and money. All of America’s industry has been built on the U.S. customary units or the old British imperial system, and all the country’s workers are trained to deal with those units. Every time the idea has been brought up in Congress, it has been quickly shot down by both the business community and the American public who aren’t keen on the time-consuming and expensive process of converting the country’s entire infrastructure. In case you are wondering or might have forgotten… 1 acre = 0.40459 hectares and or 1 hectare = 2.47105 acres. (Sources: World Atlas, Science Trends, RootsWeb, Wiki)
