Conversion of units
comparison of various scales
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.
Unit conversion is often easier within a metric system such as the SI than in others, due to the system's coherence and its metric prefixes that act as power-of-10 multipliers.
Overview
The definition and choice of units in which to express a quantity may depend on the specific situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards. Engineering judgment may include such factors as:
the precision and accuracy of measurement and the associated uncertainty of measurement
the statistical confidence interval or tolerance interval of the initial measurement
the number of significant figures of the measurement
the intended use of the measurement, including the engineering tolerances
historical definitions of the units and their derivatives used in old measurements; e.g., international foot vs. US survey foot.
For some purposes, conversions from one system of units to another are needed to be exact, without increasing or decreasing the precision of the expressed quantity. An adaptive conversion may not produce an exactly equivalent expression. Nominal values are sometimes allowed and used.
“Conversion of units” enters the record as comparison of various scales. Crown Archives preserves that source wording while asking what Conversion, units and comparison can confirm, complicate or overturn.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Mar 16, 2026. The linked authority identifier is Q618655. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Conversion of units” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.