Unit of measurement
Standardized quantities enabling consistent measurement across time and place.
Last updated
A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, used as a standard for measurement of the same kind of quantity. Any other quantity of that kind can be expressed as a multiple of the unit. For example, the metre is a unit of length representing a predetermined length, so "10 metres" means ten times that standard length. Units of measurement have played a crucial role in human endeavor from early ages to the present, with a multitude of systems once common, now largely replaced by the global standard, the International System of Units (SI).
History
Historically, units were among the earliest tools invented by humans, used for constructing dwellings, fashioning clothing, and bartering. Before the decimal metric system was established in France during the French Revolution, many units of length were based on parts of the human body. The earliest known uniform systems of measurement appeared in the 4th and 3rd millennia BC among ancient peoples of Mesopotamia, Egypt, the Indus Valley, and possibly Elam. Weights and measures are mentioned in the Bible, commanding honest and fair measures.
The Magna Carta of 1215 decreed one measure for wine, ale, and corn throughout the realm. The systematic effort for a universal system began in 1790 when the French National Assembly tasked the French Academy of Sciences with creating one. This led to the metric system, which gained international acceptance after the Metric Convention Treaty of 1875, signed by 17 nations, establishing the General Conference of Weights and Measures (CGPM). The CGPM produced the current SI, adopted in 1954.
Today, the United States remains a dual-system society, using both SI and the US Customary System. Metrology is the science of developing nationally and internationally accepted units, essential for reproducibility in science. The International Bureau of Weights and Measures (BIPM) ensures worldwide uniformity and traceability to SI. In trade, governments regulate weights and measures for fairness and transparency.
Quick Facts
- Field
- Metrology
- Earliest known use
- 4th and 3rd millennia BC among ancient peoples of Mesopotamia, Egypt, and the Indus Valley
- Modern standard
- International System of Units (SI)
- Governing body
- International Bureau of Weights and Measures (BIPM)
Facts from the source article.
Lore & Background
Units of measurement were among the earliest tools invented by humans. Primitive societies needed rudimentary measures for tasks such as constructing dwellings, fashioning clothing, or bartering food or raw materials. Before the establishment of the decimal metric system in France during the French Revolution in the late 18th century, many units of length were determined by the size of parts of the human body.
The earliest known uniform systems of measurement seem to have been created in the 4th and 3rd millennia BC among the ancient peoples of Mesopotamia, Egypt, and the Indus Valley, and perhaps also Elam in Persia. Weights and measures are mentioned in the Bible (Leviticus 19:35–36) as a commandment to be honest and have fair measures. In the Magna Carta of 1215, King John agreed to standard measures for wine, ale, corn, and cloth throughout the realm.
Reader's Guide
The definition, agreement, and practical use of units of measurement have played a crucial role in human endeavor from early ages up to the present. A multitude of systems of units used to be very common; now there is a global standard, the International System of Units (SI), which is the modern form of the metric system. Metrology is the science of developing nationally and internationally accepted units of measurement.
In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. Reproducibility of experimental results is central to the scientific method, and a standard system of units facilitates this. Scientific systems of units are a refinement of the concept of weights and measures historically developed for commercial purposes. The systematic effort to develop a universally acceptable system of units dates back to 1790 when the French National Assembly charged the French Academy of Sciences to come up with such a unit system.
This system was the precursor to the metric system, which did not take on universal acceptance until 1875 when The Metric Convention Treaty was signed by 17 nations. The CGPM produced the current SI, adopted in 1954 at the 10th Conference of Weights and Measures. The United States is the only industrialized country that has not yet at least mostly converted to the metric system, currently using both SI and the US Customary system.
Frequently Asked Questions
What exactly is a unit of measurement?
It is a fixed, agreed-upon magnitude of a particular quantity—established either by convention or by law—that serves as the reference point against which all other quantities of the same kind are expressed as multiples.
How far back do units of measurement go?
The earliest known use dates to the 4th and 3rd millennia BC, when peoples in Mesopotamia, Egypt, and the Indus Valley relied on standardized measures for trade and construction. Over millennia, many regional systems coexisted before most were phased out in favor of a single global framework.
Which academic field studies units of measurement?
The discipline is called metrology, and it encompasses the science of measurement, the development of standards, and the governance bodies—like the BIPM—that keep those standards current and universally applicable.
More in Units & Measurement
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Unit of measurement (CC BY-SA 4.0).
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced