Combining Numerals and Words - Numbers and Percentages

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

Combining Numerals and Words
Numbers and Percentages

Use a combination of numerals and words to express rounded large numbers and consecutive numerical expressions.

18.3.1 Rounded Large Numbers.

Rounded large numbers, such as those starting with million, should be expressed with numerals and words.

The disease affects 5 million to 6 million people. (Note that the word million is repeated to avoid ambiguity.)

The word million signifies the quantity 106, whereas billion signifies the quantity 109. Although billion has traditionally signified 1012 (1 million million) in Britain, many British medical journals2 have used billion to indicate the quantity 109. A number may be expressed in million rather than billion if the latter term could create ambiguity. In that case, the decimal should be moved 3 places to the right. Trillion should be used to denote the quantity 1012.

The projected budget is £2.5 billion.

Or: The projected budget is £2500 million.

The budget deficit is expected to expand to $1 trillion by 2020.

18.3.2 Consecutive Numerical Expressions.

When 2 numbers appear consecutively in a sentence, either reword the sentence or spell out 1 of the numbers for clarity.

Study participants were provided twenty 5-mL syringes.


In the cohort of 1500, 690 were men.


In the cohort of 1500 individuals, 690 were men.


In the cohort, 690 of the 1500 individuals were men.

When I first started out as an author, one had to send an envelope with 3 copies of a manuscript and one 3.5-in diskette to submit a manuscript for publication.

However, numerals may be listed consecutively if they refer to items in an array. As always, clarity and common sense should guide usage.


The life expectancy of groups 1, 2, and 3 was 69, 83, and 75 years, respectively.


The life expectancy was 69 years in group 1, 83 years in group 2, and 75 years in group 3.

Abbreviations or symbols may follow numbers. In this case, if there is potential for misunderstanding, it is preferable to reword the sentence.


There are 2 D2 dopamine receptor isoforms.


The D2 dopamine receptor has 2 isoforms.


The investigators were able to identify 3 γ-aminobutyric acid—mediated sites.


The investigators were able to identify 3 sites mediated by γ-aminobutyric acid.

Superscripts that indicate references may be mistaken for exponents if they immediately follow a numeral.

Increased morbidity has been associated with a body mass index less than 182 and greater than 27.3 [This can be reworded: Smith and Jones2 found that a body mass index of less than 18 was associated with increased morbidity. They also found that patients with a BMI greater than 27 had increased morbidity.3]