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  單位換算過程與使用者具體情況和預期目的相關。可能受法令、合同、技術規格或其它出版物技術標準的限制。工程判斷可能包括以下因素:  某些從一個單位系統需要不增減精度地向另一個單位體系嚴密轉換第一個量度。有時被稱為“軟轉換”。它不涉及更改被計量的物理配置。  與之相比,“硬轉換”或“適應轉換”可能不完全相等。它更改計量以適合在新體系內的有效數字與單位。它有時涉及專案的稍微不同的配置或尺寸替代。有時允許並使用標稱值。

  此條目內不列出在公制單位國際單位制詞頭間的轉換(例如:1 千克 = 1000 克, 1 毫克 = 0.001 克)。除非單位還有其他常見名稱。

  各表內的單位以其英文字詞的字母順序列出,突出顯示SI單位(基本單位或匯出單位)。

  此條目給出列於索引內的各個物理量數值轉換系數列表。各物理量不同單位的數值以相應的SI術語表示並顯示(某些僅有歷史意義)。

  Notes:

  A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.

  "See also:" Conversion between weight (force) and mass

  Often, information entropy is measured in shannons, whereas the (discrete) storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning. Other times the bit is used as a measure of information entropy and is thus a synonym of shannon.

  The candela is the preferred nomenclature for the SI unit.

  Please note that although becquerel (Bq) and hertz (Hz) both ultimately refer to the same SI base unit (s), Hz is used only for periodic phenomena, and Bq is only used for stochastic processes associated with radioactivity.

  The roentgen is not an SI unit and the NIST strongly discourages its continued use.

  Although the definitions for sievert (Sv) and gray (Gy) would seem to indicate that they measure the same quantities, this is not the case. The effect of receiving a certain dose of radiation (given as Gy) is variable and depends on many factors, thus a new unit was needed to denote the biological effectiveness of that dose on the body; this is known as the equivalent dose and is shown in Sv. The general relationship between absorbed dose and equivalent dose can be represented as where "H" is the equivalent dose, "D" is the absorbed dose, and "Q" is a dimensionless quality factor. Thus, for any quantity of "D" measured in Gy, the numerical value for "H" measured in Sv may be different.

  Home and office computers come with converters in bundled spreadsheet applications or can access free converters via the Internet. Units and measurements can be easily converted using these tools, but only if the units are explicitly defined and the conversion is compatible (e.g., cmHg to kPa).

  When a measure is converted to another unit in a fiction work like a novel or film, the value often loses meaning (as in numerology) or gets too many significant digits ("40 miles" turns into "64 km"). For this reason, authors sometimes choose numbers that can be converted easily. Most notably, distances measured in miles often begin with 3 or 5, so the value ghjcfugffyhfdfgjvcgconverted to km also has one significant digit (5 or 8).
單位換算是指通過乘以換算係數實現不同計量單位間的等量換算。