Products and Quotients of Unit Symbols - AMA Manual of Style
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# Products and Quotients of Unit Symbols

Chapter:
Units of Measure
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## Products and Quotients of Unit Symbols

The product of 2 or more SI units should be indicated by a space between them or by a raised multiplication dot. The multiplication dot must be positioned properly to distinguish it from a decimal point, which is set on the baseline. (See 21.6, Mathematical Composition, Expressing Multiplication and Division.) When the unit of measure is the product of 2 or more units, either abbreviations (symbols) or nonabbreviated units should be used. Abbreviated and nonabbreviated forms should not be combined in products.

 Preferred: newton meter is expressed as newton meter or N m or N · m Avoid: newton · m or N · meter

When numerals are used to denote a quantity of measurement, it is preferable to use the abbreviated form of the SI unit.

 Preferred: 50 N · m Avoid: 50 newton meter

The quotient of SI unit symbols may be expressed by the forward slash or virgule (/) or by the use of negative exponents. If the derived unit is formed by 2 abbreviated units of measure (eg, μg/L), the quotient also may be expressed by means of the forward slash or negative exponents.

 Preferred: μg/L or μg L−1 or μg · L−1 Avoid: μg per L

When the unit names are spelled out in a quotient or in text, the word per should be used.

 Preferred: The power output was measured in joules per second. Avoid: The power output was measured in joules/second [or J/s].

Expressions with 2 or more units of measure may require use of the forward slash, dot products, negative exponents, or parentheses. (See 21.6, Mathematical Composition, Expressing Multiplication and Division.)

mL · kg−1 · min−1 or mL/kg/min

m2 · kg · s−2 · A−2 or (m2 · kg)/(s2 · A2)