# Unit of measurement

unitunits of measurementweights and measuresunitsunit of measureunits of measurephysical unitmeasurementphysical unitsmeasures
A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity.wikipedia
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### Metre

metermmetres
The metre is a unit of length that represents a definite predetermined length.
The SI unit symbol is m.

### Physical quantity

physical quantitiesquantitiesquantity
For example, a length is a physical quantity.
A physical quantity can be expressed as the combination of a magnitude and a unit.

### Metrology

metrologicalmetrologistlegal metrology
Metrology is the science of developing nationally and internationally accepted units of measurement.
The sub-fields are scientific or fundamental metrology, which is concerned with the establishment of units of measurement, Applied, technical or industrial metrology, the application of measurement to manufacturing and other processes in society, and Legal metrology, which covers the regulation and statutory requirements for measuring instruments and the methods of measurement.

### Measurement

measuremeasuringmeasurements
In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful.
Units of measurement are generally defined on a scientific basis, overseen by governmental or independent agencies, and established in international treaties, pre-eminent of which is the General Conference on Weights and Measures (CGPM), established in 1875 by the Metre Convention, overseeing the International System of Units (SI) and having custody of the International Prototype Kilogram.

### Dimensional analysis

dimensiondimensionsdimensionally equivalent
The judicious selection of the units of measurement can aid researchers in problem solving (see, for example, dimensional analysis).
In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms) and tracking these dimensions as calculations or comparisons are performed.

### Length

For example, a length is a physical quantity.
There are several units that are used to measure length.

### Metric system

metricmetric unitsmetric unit
Now there is a global standard, the International System of Units (SI), the modern form of the metric system. Systems of measurement in modern use include the metric system, the imperial system, and United States customary units.
Designed for transnational use, it consisted of a basic set of units of measurement, now known as base units.

### Unit prefix

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One way to make large numbers or small fractions easier to read, is to use unit prefixes.
A unit prefix is a specifier or mnemonic that is prepended to units of measurement to indicate multiples or fractions of the units.

### Inch

ininchesinternational inch
For example, an inch could be defined in terms of a barleycorn.
The inch (abbreviation: in or ″) is a unit of length in the (British) imperial and United States customary systems of measurement.

### Scientific method

scientific researchscientificmethod
Reproducibility of experimental results is central to the scientific method.
Scientific quantities are often characterized by their units of measure which can later be described in terms of conventional physical units when communicating the work.

### SI base unit

base unitSI base unitsbase units
In this SI units system, there are seven SI base units and three supplementary units.
The SI base units are seven units of measure defined by the International System of Units as the basic set from which all other SI units can be derived.

### Physics

physicistphysicalphysicists
In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful.
The results from physics experiments are numerical data, with their units of measure and estimates of the errors in the measurements.

### International System of Units

SISI unitsSI unit
Now there is a global standard, the International System of Units (SI), the modern form of the metric system.

### United States customary units

USUS customary unitsU.S. customary units
Systems of measurement in modern use include the metric system, the imperial system, and United States customary units. Both the imperial units and US customary units derive from earlier English units.
United States customary units are a system of measurements commonly used in the United States.

### English units

English unitEnglishEnglish system
Both the imperial units and US customary units derive from earlier English units.
English units are the units of measurement that were used in England up to 1826 (when they were replaced by Imperial units), which evolved as a combination of the Anglo-Saxon and Roman systems of units.

### Metrication

Some steps towards US metrication have been made, particularly the redefinition of basic US and imperial units to derive exactly from SI units.
Worldwide, there has been a process of nations transitioning from their various local and traditional units of measurement, to the metric system.

### Natural units

natural unitGeometric variableshas been set to one
Systems of units based on these are called natural units.
In physics, natural units are physical units of measurement based only on universal physical constants.

### System of measurement

Systems of measurementsystem of unitsHistorical weights and measures
A multitude of systems of units used to be very common.
A system of measurement is a collection of units of measurement and rules relating them to each other.

### List of unusual units of measurement

football fieldfull-lengthDog year
Also a great number of unusual and non-standard units may be encountered.
An unusual unit of measurement is a unit of measurement that does not form part of a coherent system of measurement; especially in that its exact quantity may not be well known or that it may be an inconvenient multiple or fraction of base units in such systems.

### Weights and Measures Acts (UK)

Weights and Measures ActWeights and Measures Act 1985Weights and Measures Act 1824
To reduce the incidence of retail fraud, many national statutes have standard definitions of weights and measures that may be used (hence "statute measure"), and these are verified by legal officers.
Weights and measures acts are acts of the British Parliament determining the regulation of weights and measures.

### Conversion of units

conversion factorunit conversionConversions
Conversion of units involves comparison of different standard physical values, either of a single physical quantity or of a physical quantity and a combination of other physical quantities.
Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors.

### Standardization

standardstandardizedstandards
An important feature of modern systems is standardization.
He invented the current balance, also known as the Kelvin balance or Ampere balance (SiC), for the precise specification of the ampere, the standard unit of electric current.

### Pound (force)

lbflb f pound-force
One example of the importance of agreed units is the failure of the NASA Mars Climate Orbiter, which was accidentally destroyed on a mission to Mars in September 1999 instead of entering orbit due to miscommunications about the value of forces: different computer programs used different units of measurement (newton versus pound force).
The pound of force or pound-force (symbol: lbf, sometimes lb f, ) is a unit of force used in some systems of measurement including English Engineering units and the Foot–pound–second system.

### List of humorous units of measurement

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Many people have made use of, or invented, units of measurement intended primarily for their humor value.

### List of obsolete units of measurement

obsolete British weight measurewas
These units of measurement are typically no longer used, though some may be in limited use in various regions.