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SI multiples[国际单位进度表]

 

 

Main article: Orders of magnitude (mass)

 

Because SI prefixes may not be concatenated (serially linked) within the name or symbol for a unit of measure, SI prefixes are used with the gram, not the kilogram, which already has a prefix as part of its name.^[79] For instance, one-millionth of a kilogram is 1 mg (one milligram), not 1 µkg (one microkilogram).

 

SI multiples for gram (g)

 

Submultiples				Multiples
Value	SI symbol	Name		Value	SI symbol	Name
10−1 g	dg	decigram		101 g	dag	decagram
10−2 g	cg	centigram		102 g	hg	hectogram
10−3 g	mg	milligram		103 g	kg	kilogram
10−6 g	µg	microgram		106 g	Mg	megagram (tonne)
10−9 g	ng	nanogram		109 g	Gg	gigagram
10−12 g	pg	picogram		1012 g	Tg	teragram
10−15 g	fg	femtogram		1015 g	Pg	petagram
10−18 g	ag	attogram		1018 g	Eg	exagram
10−21 g	zg	zeptogram		1021 g	Zg	zettagram
10−24 g	yg	yoctogram		1024 g	Yg	yottagram
Common prefixed units are in bold face.[Note 23]

 

• The microgram is typically abbreviated "mcg" in pharmaceutical and nutritional supplement labelling, to avoid confusion, since the "µ" prefix is not always well recognized outside of technical disciplines.^{[Note 24]} (The expression "mcg" is also the symbol for an obsolete CGS unit of measure known as the "millicentigram", which is equal to 10 µg.)
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• In the UK, because serious medication errors have been made from the confusion between milligrams and micrograms when micrograms has been abbreviated, the recommendation given in the Scottish Palliative Care Guidelines is that doses of less than one milligram must be expressed in micrograms and that the word microgram must be written in full, and that it is never acceptable to use "mcg" or "μg".
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• The decagram (dag in SI) is in much of Europe often abbreviated "dkg" (from the local spelling "dekagram") and is used for typical retail quantities of food (such as cheese and meat).
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• The unit name "megagram" is rarely used, and even then typically only in technical fields in contexts where especially rigorous consistency with the SI standard is desired. For most purposes, the name "tonne" is instead used. The tonne and its symbol, "t", were adopted by the CIPM in 1879. It is a non-SI unit accepted by the BIPM for use with the SI. According to the BIPM, "In English speaking countries this unit is usually called 'metric ton'."^[80] The unit name "megatonne" or "megaton" (Mt) is often used in general-interest literature on greenhouse gas emissions, whereas the equivalent unit in scientific papers on the subject is often the "teragram" (Tg).