Use this Conversion Calculator to convert between common units. Select the current unit in the left column, the target unit in the right column, and a value in the left column to generate the resulting conversion.

Different Systems of Units

Historically, many different systems of units have been employed, with a system of units defined as a collection of units of measurement with rules that link them together. A unit of measurement is a determined magnitude of a quantity that serves as a standard for measuring similar quantities, such as length, weight, and volume.

Historically, many measurement systems were defined at the local level and may be based on factors as arbitrary as the length of a king’s thumb. While this may work on a small scale, having systems of units based on units that others may not be able to relate to or understand complicates interaction in both trade and science. As a result, the development of more general and uniform systems occurred over time. Some of the current unit systems in use are the metric system, the imperial system, and the United States customary units.

The International System of Units (SI) is the current metric standard, consisting of seven SI base units: length, mass, time, temperature, electric current, luminous intensity, and amount of substance. Although SI is virtually generally used in science (even in the United States), certain countries, such as the United States, continue to use their own system of measurement. This is due in part to the significant financial and cultural expenses associated with altering a measurement system vs the possible advantage of employing a standardized method.  Because US customary units (USC) are so entrenched in the United States, and SI is already employed in most applications where standardization is critical, everyday usage of USC remains common in the United States and is unlikely to change. As a result, several unit converters, such as this Conversion Calculator, exist and will continue to exist in order for people all over the world to successfully communicate different measurements.

History of the Pound

In the eighth and ninth centuries of the Common Era (CE), Arab civilization thrived in the Middle East and Spain. The Arabs employed coins to measure units of weight because a struck coin could not be easily chopped or shaved to lessen its weight, providing a measurable standard. As a basic unit of measurement, they used a coin known as a silver dirhem, which weighed approximately 45 fully grown grains of barley. A Wukryeh was made up of ten dirhems and was translated into Latin as a “uncia” (the origin of the term “ounce.”

Over time, trade expanded from the Mediterranean to Europe, including the northern German city states. As a result, a pound, 16 ounces of silver, or 7200 grains, became a widely used unit of measurement in many places.

While England adopted this measure, a silver scarcity prompted King Offa to lower the pound’s size to 5400 grains in order to utilize smaller coins. When William the Conqueror became King of England, he kept the 5400-grain pound for minting coins but switched to the 7200-grain pound for other purposes.

Though many countries, including England, used the pound from that point forward (the British pound sterling, or GBP, was equal to one pound-weight of silver in King Offa’s time), the avoirdupois weight system was adopted during Queen Elizabeth’s reign in the 16th century. It was a coal-weighting system whose name was derived from the French term “avoir de pois” (weighted commodities or property). The avoirdupois represented 7,000 grains, 256 drams of 27.344 grains, or 16 ounces of 437 ½ grains apiece. Since 1959, most English-speaking countries have officially defined the avoirdupois pound as 0.45359237 kilos.

Different measurement systems also evolved over time in Asian countries. For example, in ancient India, a weight unit known as the “Satamana” was employed, which was equivalent to the weight of 100 gunja berries. Shi Huang Di, China’s first emperor, developed a system of weights and measures in the third century BCE (Before the Common Era). The weight was calculated using the shi, which was roughly 132 pounds. The Chi and Zhang were length units of roughly 25 centimeters (9.8 inches) and 3 meters (9.8 feet), respectively. The Chinese also devised a method to verify precision by using a certain size bowl for measures that made a specific sound when struck; if the sound was off pitch, the measurement was inaccurate.

Brief History of the Metric System

In 1668, John Wilkins proposed a decimal system in which length, area, volume, and mass were connected to one another via a pendulum with a one-second beat as the basic unit of length. Gabriel Mouton developed a decimal system based on the circumference of the earth in 1670, which was supported by other renowned scientists at the time, including Jean Picard and Christiaan Huygens, but it did not catch on for another 100 years.

By the mid-eighteenth century, nations that traded and shared scientific ideas recognized the importance of standardizing weights and measurements. In 1790, Charles Maurice de Talleyrand-Perigord, the Prince of Talleyrand, addressed the British (represented by John Riggs-Miller) and the Americans (represented by Thomas Jefferson) with ideas to create a common length standard based on the length of a pendulum. In the same year, Thomas Jefferson submitted the “Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States,” which argued for a decimal system in which units were related to one another using powers of ten. A committee formed in France composed of some of the most important scientists of the time reached a similar result and suggested a decimal system for all weights and measurements. Congress reviewed Jefferson’s report, but it was not approved. John Riggs-Miller lost his British Parliamentary seat in the 1790 election. As a result, the measurement system was only used in France, where it was fully defined by law in 1795.  However, it was not until 1799 that the metric system was formally introduced in France, and it was still not widely used throughout the country.

The metric system developed slowly, and the first areas to adopt it were those acquired by France during Napoleon’s reign. By 1875, two-thirds of the European population and nearly half of the global population had embraced the metric system. In 1920, around 22% of the global population used the imperial or US customary systems, 25% primarily used the metric system, and 53% did not use either.

The International System of Units, which is now the most extensively used system of measurement, was published in 1960. It has been accepted by all industrialized countries except the United States, yet, as previously said, it is widely used in research and the military, including in the United States.