The creation of the decimal Metric System at the time of the French Revolution and the subsequent deposition of two platinum standards representing the meter and the kilogram, on 22 June 1799, in the Archives de la République in Paris can be seen as the first step in the development of the present International System of Units.
In 1832, Gauss strongly promoted the application of this Metric System, together with the second defined in astronomy, as a coherent system of units for the physical sciences. Gauss was the first to make absolute measurements of the earth’s magnetic force in terms of a decimal system based on the three mechanical units millimeter, gram and second for, respectively, the quantities length, mass and time. In later years, Gauss and Weber extended these measurements to include electrical phenomena
These applications in the field of electricity and magnetism were further developed in the 1860s under the active leadership of Maxwell and Thomson through the British Association for the Advancement of Science (BAAS). They formulated the requirement for a coherent system of units with base units and derived units. In 1874 the BAAS introduced the CGS system, a three-dimensional coherent unit system based on the three mechanical units centimeter, gram and second, using prefixes ranging from micro to mega to express decimal submultiples and multiples. The following development of physics as an experimental science was largely based on this system.
The sizes of the coherent CGS units in the fields of electricity and magnetism, proved to be inconvenient so, in the 1880s, the BAAS and the International Electrical Congress, predecessor of the International Electrotechnical Commission (IEC), approved a mutually coherent set of practical units. Among them were the ohm for electrical resistance, the volt for electromotive force, and the ampere for electric current.
After the establishment of the Meter Convention on May, 20 1875 the CIPM concentrated on the construction of new prototypes taking the meter and kilogram as the base units of length and mass. In 1889 the 1st CGPM sanctioned the international prototypes for the meter and the kilogram. Together with the astronomical second as unit of time, these units constituted a three-dimensional mechanical unit system similar to the CGS system, but with the base units meter, kilogram and second.
In 1901 Giorgi showed that it is possible to combine the mechanical units of this meter–kilogram–second system with the practical electric units to form a single coherent four-dimensional system by adding to the three base units, a fourth base unit of an electrical nature, such as the ampere or the ohm, and rewriting the equations occurring in electromagnetism in the so-called rationalized form. Giorgi’s proposal opened the path to a number of new developments.
After the revision of the Meter Convention by the 6th CGPM in 1921, which extended the scope and responsibilities of the BIPM to other fields in physics, and the subsequent creation of the CCE (now CCEM) by the 7th CGPM in 1927, the Giorgi proposal was thoroughly discussed by the IEC and the IUPAP and other international organizations. This led the CCE to recommend, in 1939, the adoption of a four-dimensional system based on the meter, kilogram, second and ampere, a proposal approved by the ClPM in 1946.
Following an international inquiry by the BIPM, which began in 1948, the 10th CGPM, in 1954, approved the introduction of the ampere, the kelvin and the candela as base units, respectively, for electric current, thermodynamic temperature and luminous intensity. The name International System of Units (SI) was given to the system by the 11th CGPM in 1960. At the 14th CGPM in 1971 the current version of the SI was completed by adding the mole as base unit for amount of substance, bringing the total number of base units to seven.
LENGTH UNITS
Inch Unit
The inch is an ancient unit of length, originating from the Roman "uncia" and later defined in medieval England as three barleycorns. It evolved through centuries of use and standardization, notably being set as 2.54 centimeters in 1959. Today, it remains a widely used measure in English-speaking countries for various practical applications.
Millimeter Unit
The millimeter, a unit in the metric system, was introduced during the French Revolution as part of a push for a universal measurement system. It was defined as one-thousandth of a meter, which itself was based on the Earth’s meridian. Adopted globally, it’s now essential for precision in fields like science, engineering, and industry.
Feet Unit
The foot is an ancient unit of length, originating from measurements based on the human foot. Used by the Egyptians, Greeks, and Romans, it became standardized in medieval Europe, notably defined by England as 12 inches in the 12th century. The foot has been crucial for everyday measurements and construction, remaining a key unit in countries like the US today.
Meter Unit
The meter, defined during the French Revolution in 1791, was based on one ten-millionth of the distance from the equator to the North Pole along a meridian. It became the cornerstone of the metric system, designed for universal use and precision, and is now defined by the distance light travels in a vacuum in 1/299,792,458 of a second, making it fundamental in science and international measurement standards.
Yard Unit
The yard, originating from ancient measurements, was formalized in medieval England as the distance from King Henry I's nose to his outstretched thumb, approximately three feet. It became a standard unit in English-speaking countries, used for land measurement and everyday purposes, and was internationally defined in 1959 as exactly 0.9144 meters.
Mile Unit
The mile, rooted in Roman times as "mille passus" or "thousand paces" (approximately 1,480 meters), evolved through medieval Europe and was standardized in England in the late 16th century as 5,280 feet or 1,760 yards. It remains a key unit for distance measurement in the US and UK, used in contexts like road travel and land area.
Kilometer Unit
The kilometer, introduced during the French Revolution in the late 18th century, is part of the metric system and equals one thousand meters. Designed to provide a universal and rational system of measurement, the kilometer is widely used around the world today for measuring long distances, especially in transportation and geography.
AREA UNITS
Square Inches Unit
Square inches, a unit for measuring area, originated in ancient times with the inch itself. Its modern use was formalized in England during the development of the Imperial system, where it measures an area of one inch by one inch. Widely used in the US and UK, it is essential for small-scale measurements in crafts, engineering, and construction.
Square Millimeters Unit
The square millimeter, a metric unit for measuring small areas, was introduced during the French Revolution alongside the metric system. It represents an area of one millimeter by one millimeter and is essential for precise measurements in science, engineering, and industry, reflecting the metric system's global adoption for its ease and uniformity in measurement.
Square Feet Unit
Square feet, a unit of area measurement, originated from ancient systems where the foot was a standard length unit. It became formalized in medieval England as the area of a square with each side measuring one foot. Widely used in the US and UK, square feet are crucial for measuring building spaces and land areas, integral to real estate and construction industries.
Square Meter Unit
The square meter, introduced during the French Revolution, is the metric system's unit for area, defined as the area of a square with one-meter sides. It was created to provide a universal, consistent measurement system, and is now the global standard for measuring large areas in fields like architecture, real estate, and land management, reflecting the metric system's widespread adoption for its simplicity and precision.
Square Yard Unit
The square yard, a unit of area measurement, originated in medieval England and represents the area of a square with each side measuring one yard. It was widely used in agriculture and land division and remains relevant today in the US and UK for measuring land, flooring, and textiles, despite the increasing use of metric measurements.
Square Mile Unit
The square mile, a unit of area measurement, dates back to Roman times and evolved with the mile itself. It was formalized in England to measure expansive land areas, representing one mile by one mile. Today, it is used in the US and UK for large-scale geographical and urban planning, reflecting historical land division practices and aiding in the management of large territories.
Acre Unit
The acre, an ancient unit of area, originated in medieval England as the amount of land that could be plowed by one man with an ox in a day. Traditionally defined as 66 feet by 660 feet, it was standardized in the 16th century to 43,560 square feet. Today, it's widely used in the US and UK for measuring agricultural land and real estate, reflecting its historical roots in farming and land management.
Hectare Unit
The hectare, introduced during the French Revolution with the metric system, is a unit of area equivalent to 10,000 square meters or 100 ares. Designed for simplicity and universality, it became the standard for large land areas, particularly in agriculture and land management, and is widely used globally, especially in countries adopting the metric system for its ease of use and consistency.
Square Kilometer Unit
The square kilometer, a metric unit of area measurement, was introduced during the French Revolution as part of the metric system. Defined as the area of a square with each side measuring one kilometer (1,000 meters), it facilitates the measurement of vast areas like countries and regions. Widely adopted globally, it reflects the metric system's emphasis on standardization and precision in geographic and land management contexts.
VOLUME UNITS
Fluid Ounces Unit
Fluid ounces, a unit of volume, trace back to ancient Roman times where they were used to measure liquid capacities. The unit was refined in medieval England to denote 1/20th of a pint in the US and 1/160th of a gallon in the UK. Today, fluid ounces are used in both systems for measuring small liquid volumes, crucial in cooking, medicine, and various industries, reflecting historical measurement practices and regional variations.
Milliliter Unit
Milliliters, a metric unit of volume, emerged during the French Revolution as part of the metric system's push for standardization. Defined as one-thousandth of a liter, it became widely adopted globally for its simplicity and precision in measuring small volumes of liquids, essential in medicine, science, and everyday use.
Gallon Unit
The gallon, a unit of measurement for volume, has evolved over time. Originating from medieval England, it was defined as the volume of eight pounds of wheat. In 1824, the British Imperial gallon was standardized as the volume of 10 pounds of distilled water under specified conditions. Later, the United States adopted a slightly smaller gallon, the US liquid gallon, defined in 1836 as the volume of 231 cubic inches, which remains in use today.
Liter Unit
The liter, a metric unit of volume, was introduced during the French Revolution in 1795 as part of the metric system. It was originally defined as the volume occupied by one cubic decimeter, which is a cube with sides of 0.1 meters. The liter has since become a globally accepted standard for measuring liquid volumes, particularly in science, industry, and everyday use.
Cubic Feet Unit
The cubic foot, a unit of volume, has been used since ancient times, likely originating from measuring the volume of grain bins or containers. It's defined as the volume of a cube with sides one foot long. Standardized during the Middle Ages, it remains a common unit in architecture, engineering, and everyday measurements, particularly in the United States and countries influenced by British imperial units.
Cubic Meter Unit
The cubic meter, a fundamental unit of volume in the metric system, was established during the French Revolution in 1795 as part of the metric system's adoption. It's defined as the volume of a cube with sides one meter long. Widely used worldwide in science, engineering, and commerce, the cubic meter is a standard for measuring large volumes of liquids, gases, and solid materials.
Cubic Yard Unit
The cubic yard, a unit of volume, dates back to medieval England, where it was used for measuring quantities of materials like grain or stone. It's defined as the volume of a cube with sides one yard long. Standardized in the United States and the United Kingdom, it remains common in construction, landscaping, and other industries for measuring large volumes of materials.
MASS UNITS
Ounces Unit
The ounce, a unit of mass or weight, has ancient origins dating back to various civilizations using different standards. The avoirdupois ounce, standardized in medieval England, equals 1/16 of a pound and is commonly used in the United States for measuring both weight and volume (fluid ounces).
Gram Unit
The gram, a metric unit of mass, was established during the French Revolution in 1795 as part of the metric system. It's defined as the mass of one cubic centimeter of water at its maximum density. Widely adopted globally, the gram is a standard unit for measuring small masses in scientific, industrial, and everyday contexts.
Pound Unit
The pound, a unit of weight or mass, has a long history originating from ancient Rome. It was standardized as a unit of weight in medieval England, originally defined as the weight of 240 silver pennies. Over time, it evolved into different systems such as the avoirdupois pound (16 ounces), commonly used in the United States, and the troy pound (12 ounces), used for precious metals.
Kilogram Unit
The kilogram, a fundamental unit of mass in the metric system, was established during the French Revolution in 1795. It was originally defined as the mass of one liter of water at its maximum density. The kilogram has since become a globally accepted standard for measuring mass, replacing older systems based on physical artifacts with the adoption of the International Prototype of the Kilogram (IPK) in 1889 and its redefinition based on fundamental constants in 2019.
Short-Ton Unit
The short ton, a unit of weight commonly used in the United States, is equivalent to 2,000 pounds. It originated from the British long ton, which is 2,240 pounds, and was standardized in the United States in the early 20th century for trade and industrial purposes. The short ton remains a standard measure in industries such as shipping, mining, and agriculture across the United States.
Mega Gram Unit
The megagram, often abbreviated as Mg, is a unit of mass in the metric system equivalent to one million grams or 1,000 kilograms. It is commonly used in scientific and industrial contexts, particularly for large-scale measurements of weight or mass. The term "megagram" is derived from the Greek word "mega," meaning large or great, reflecting its magnitude compared to smaller metric units like grams and kilograms.
TEMPERATURE UNITS
Celsius Unit
The Celsius temperature scale, also known as the centigrade scale, is named after its Swedish inventor, Anders Celsius. It was introduced in 1742 and is based on dividing the freezing and boiling points of water into 100 equal degrees. It's widely used globally, with 0°C as the freezing point and 100°C as the boiling point of water at sea level under standard atmospheric pressure.
Fahrenheit Unit
The Fahrenheit temperature scale, developed by Daniel Gabriel Fahrenheit in the early 18th century, divides the freezing and boiling points of water into 180 equal divisions. 32°F is the freezing point and 212°F is the boiling point of water at standard atmospheric pressure. It remains in use primarily in the United States and a few other countries, alongside the Celsius scale used worldwide.
CURRENCY UNITS
USD Currency
The United States dollar (USD) has a rich history dating back to 1792 when it was officially adopted as the country's currency. It has since become one of the world's dominant reserve currencies, widely used in international trade and finance. The USD's value is managed by the Federal Reserve, impacting global economies and financial markets due to its stability and widespread acceptance.
EURO Currency
The euro (€) was introduced on January 1, 1999, as an electronic currency for financial transactions, and later as physical notes and coins in 2002. It replaced the former national currencies of 19 of the 27 European Union member countries, promoting economic integration and stability across Europe. The euro is managed by the European Central Bank (ECB) and has become the second most traded currency in the world after the US dollar.