Numbers and measurements

There are several acceptable ways to describe ages. The unit of measure (months or years) should generally be included. The following are just a few examples:

• Infants less than 6 months old.
• Children under five years of age.
• Adults aged 65 years or older.

You may use either a numeral (e.g., 5) or the word equivalent (e.g., five) for ages, as long as you are consistent within a document.

For documents intended for an international audience, be clear as to the type of currency; for example, use US$1,000 not $1,000. You may use any of the following formats as long as you are consistent: US$1,000, USD 1,000, or 1,000 USD. (Do not write 1,000US$.) Note the spacing: US$ is closed up with the numeral; USD is not: US$5 million; USD 5 million.

If the type of currency is the same throughout a document, it is fine to specify only at first use; in a formal document, you may wish to add a clarifying note. If multiple types of currency are discussed (e.g., EUR, KES, ZMW), specify the type of currency at each mention.

Currency abbreviations do not need to be defined (spelled out) in the text of a document; however, if your document has a list of abbreviations, include the currency abbreviation and definition there.

See also Ranges, below.

PATH style for dates is month day, year:

• January 3, 2023.

When all three elements are included in mid-sentence, use a comma before and after the year:

• The training session held on January 3, 2023, was the first step.

Do not use commas when only the month and year are given:

• The training session held in January 2023 was the first step.

Although an en dash is acceptable in tables and figures, avoid its use in body text whenever possible; instead, use to or through:

• The project ran from January 1 through December 31.

See also Ranges, below.

In scientific and technical documents, use decimals: 1.5 not 1½. For fractions used in narrative text to suggest approximate amounts, use words and hyphenate: two-thirds of the respondents, three-fourths of the children.

For angles and temperatures, use the proper degree symbol rather than a superscript letter or numeral. For angles, there should be no space between the numeral and the symbol: 90° angle. For temperatures, there should be no space between the numeral, the symbol, and the abbreviation for the temperature scale, whether Celsius or Fahrenheit: 37°C, 98.6°F.

See also Ranges, below.

Use commas in numbers greater than 999: 1,000, 10,000. In nontechnical and nonscientific documents, you may spell out thousand (e.g., two thousand). For very large numbers, use numerals followed by million or billion: 10 million doses, 3 billion stickers.

Use an en dash (–) rather than a hyphen (-) to indicate negative numbers (e.g., –10).

It is unnecessary to use a number sign (#) before a numeral—for example, answer 7 not answer #7.

Use numerals for percentages—for example, 2 percent, 10.5 percent.

In nontechnical documents, use percent rather than the symbol (%). In technical documents, such as articles in scientific journals, in tables and figures, and in all other instances where space is limited, you may use the symbol. Whichever you choose, be consistent.

When referring to several percentages, use the same number of decimal places; for example, 5.6 and 24.2 percent not 5.6 and 24 percent.

Be precise when describing changes in percentages. For example, an increase from 25 to 50 percent can be described as a 100 percent increase (a doubling of the percentage) or as a 25 percentage point increase but not as a 25 percent increase.

See also Ranges, below.

In text, use from . . . to, from . . . through, or between . . . and:

• Focus group size ranged from 12 to 15 participants.
• Project implementation ran from January 2021 through December 2022.
• Each committee had between 20 and 25 members.

In tables and figures, use an en dash:

• 0–6 months
• n = 12–15

If space is an issue, you may remove the space around the equal sign: n=12–15.

When there is no space between a numeral and its symbol, repeat the symbol:

$15 to $25; 15°C to 20°C; 15% to 20%

Otherwise, do not repeat the unit of measure:

15 to 20 percent; 15 to 20 mg

Avoid Roman numerals unless they are standard for a particular construction.

Whenever possible, use periods (full stops) in a.m. and p.m. and avoid capital letters or small caps. You may use a single numeral to indicate time (e.g., 8 a.m.), but be consistent. For example, indicate that a meeting be held from 8:00 to 9:30 a.m. not from 8 to 9:30 a.m.

Use metric units or both US customary units and metric equivalents whenever possible.

In technical and scientific documents, abbreviate units of measure, such as milligrams, milliliters, and kilometers: 10 mg, 5 mL, and 65 km.

Use the Greek letter mu (µ) rather than the letter u to indicate micro: µg.

The AMA Manual of Style has a comprehensive list of units of measure and their abbreviations.

To quantify simple nouns, use words for one through ten: one pharmacy, ten health care workers. Otherwise, use numerals: 11 clinics, 38 boxes.

Exceptions:

• Always spell out numbers that begin a sentence.
• For numbers that refer to the same category, if some are greater than ten and some are not, use numerals for all: We surveyed 20 hospitals, including 5 in the capital city.
• Use numerals for time points in a project or program and for other, similar constructions: Phase 3, objective 4, year 1.
• For numbers directly adjacent to each other, spell out one or the other to avoid confusion: twenty-five 2-mg capsules.
• Use numerals for measurements of weight, volume, and distance: 1 kg, 10 mL, 5 km.
• In a general narrative, use words for measurements of time: The project lasted seven years. In technical and scientific documents, use numerals for measurements of time: 3 days after treatment.

See also Ages, above.