AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Format, Style, and Punctuation
Units of Measure

The format, style, and punctuation guidelines generally apply for SI reporting but also are used for reporting most values in conventional units.

17.3.1 Exponents.

The SI reporting style uses exponents rather than certain abbreviations, such as cu and sq.

17.3.2 Plurals.

The same symbol is used for single and multiple quantities. Unit symbols are not expressed in the plural form.

17.3.3 Subject-Verb Agreement.

Units of measure are treated as collective singular (not plural) nouns and require a singular verb.

To control the patient’s fever, 500 mg of the medication was [not were] administered at the time of admission and 1000 mg was required 4 hours later.

17.3.4 Spelling Out Units of Measure.

A unit of measure that follows a number at the beginning of a sentence, title, or subtitle should not be abbreviated, even though the same unit of measure is abbreviated if it appears elsewhere in the same sentence (see 18.2.1, Beginning a Sentence, Title, Subtitle, or Heading, and 18.1.2, Common Fractions). Units of measure not immediately following a numeric value also should be spelled out.

Fifty milligrams of medication was the baseline dose, which was titrated to 100 mg.

Tumor sizes were measured in centimeters.

Hundreds of milligrams of orlistat can be absorbed under certain conditions.

17.3.5 Abbreviations.

Most units of measure are abbreviated when used with numerals or in a virgule construction. Certain units of measure should be spelled out at first mention, with the abbreviated form in parentheses. Thereafter, the abbreviated form should be used in text (see 14.12, Units of Measure).

17.3.6 Punctuation.

Symbols or abbreviations of units of measure are not followed by a period, unless the symbol occurs at the end of a sentence.

The patient’s weight was 80 kg [not 80 kg.] and had increased by 10%.

17.3.7 Hyphens.

A hyphen is used to join 2 spelled-out units of measure.

pascal-second

person-years

pack-years

Note: Capitalization for the above examples follows the style for temporary hyphenated compounds (see 10.2.2, Hyphenated Compounds) and appears as “Person-Years” in a title.

A hyphen is used to join a unit of measure and the number associated with it when the combination is used as an adjective (see 8.3.1.1, Temporary Compounds).

an 8-L container

a 10-mm strip

17.3.8 Spacing.

With the exception of the percent sign, the degree sign (for angles not temperatures), and normal and molar solutions (see 17.5.7, Solutions and Concentration), a full space should appear between the arabic numeral that indicates the quantity and the unit of measure.

140 nmol/L (not 140nmol/L)

135-150 nmol/L

3M sodium chloride

120 mm Hg

40% adherence rate

40%-50%

45° angle

temperature of 37.5 °C (not 37.5°C)

(temperature range, 38-39 °C)

Note: Ranges may use a hyphen when given in figures and tables and when given in parentheses in text.

When symbols are presented immediately adjacent to the value (eg, %), they repeat.

5%, 6%, and 7% (not 5, 6, and 7%)