Unit of measurement

A unit of measurement, or unit of measure, is a definite <a href="/facts/Magnitude_(mathematics)/KCn9PoF0">magnitude</a> of a <a href="/facts/Quantity/E2jCKetq">quantity</a>, defined and adopted by convention or by law, that is used as a standard for <a href="/facts/Measurement/rsLLbn1s">measurement</a> of the same <a href="/facts/Kind_of_quantity/S8pWBEpK">kind of quantity</a>. Any other quantity of that kind can be expressed as a multiple of the unit of measurement.
For example, a <a href="/facts/Length/EwFyAqGH">length</a> is a <a href="/facts/Physical_quantity/S8pWBEpK">physical quantity</a>. The <a href="/facts/Metre/hPhzc1CV">metre</a> (symbol m) is a unit of length that represents a definite predetermined length. For instance, when referencing "10 metres" (or 10 m), what is actually meant is 10 times the definite predetermined length called "metre".
The definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to the present. A multitude of <a href="/facts/System_of_measurement/xIsWmFWW">systems of units</a> used to be very common. Now there is a global standard, the <a href="/facts/International_System_of_Units/S7YLglNz">International System of Units</a> (SI), the modern form of the <a href="/facts/Metric_system/to24H0YK">metric system</a>.
In trade, weights and measures are often a subject of governmental regulation, to ensure fairness and transparency. The <a href="/facts/International_Bureau_of_Weights_and_Measures/tPEu4X0s">International Bureau of Weights and Measures</a> (BIPM) is tasked with ensuring worldwide uniformity of measurements and their traceability to the International System of Units (SI).
<a href="/facts/Metrology/HC0MmLdb">Metrology</a> is the science of developing nationally and internationally accepted units of measurement.
In <a href="/facts/Physics/a7aH2y08">physics</a> and metrology, units are standards for <a href="/facts/Measurement/rsLLbn1s">measurement</a> of physical quantities that need clear definitions to be useful. <a href="/facts/Reproducibility/yh5pawMj">Reproducibility</a> of experimental results is central to the <a href="/facts/Scientific_method/182j8RWE">scientific method</a>. 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.
<a href="/facts/Science/IJoaD7rs">Science</a>, <a href="/facts/Medicine/2fnp90Je">medicine</a>, and <a href="/facts/Engineering/RFVg8H3I">engineering</a> often use larger and smaller units of measurement than those used in everyday life. The judicious selection of the units of measurement can aid researchers in <a href="/facts/Problem_solving/9cuLz5pH">problem solving</a> (see, for example, <a href="/facts/Dimensional_analysis/t6UskoCD">dimensional analysis</a>).

Unit of measurement open-in-new

Unit of measurement