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Numbers

Use the conventions for writing numbers given below. Make sure to check your target journal’s guidelines first (some guidelines give specific instructions about numbers).

Small numbers

Natural numbers below 10 that are not followed by a unit should be spelled out (e.g., "two" vs. "2").

Example 1. Small numbers
example

We applied three configurations …​
example

The exact solution of the two-mode model …​
Mistake

  • The author uses numerals for small numbers.

Remedy

  • Spell out numbers below 10.

Example 2. Small numbers
incorrect

…​ with 2 models of the fixed offshore structure …​
correct

…​ with two models of the fixed offshore structure …​

Numbers in adjectives

When a number is part of an adjective, a hyphen is generally added between the number and the word that follows it.

Example 3. Adjectives that include number
example

…​ the four-point probe method was used to …​
example

…​ in the 12-parameter model …​
example

…​ second-order factor …​
Mistake

  • The author uses a number in an adjective without a hyphen.

Remedy

  • Add a hyphen to numbers in adjectives.

Example 4. Number with hyphen in adjective
incorrect

…​ the first order polynomial was …​
correct

…​ the first-order polynomial was …​

If the adjective includes a unit, the situation is not so clear. The APA style guide requires a hyphen between the number and unit; The Chicago Manual of Style and SI guidelines, in contrast, do not allow this hyphen.

Example 5. Adjectives that include number and unit
APA
example

a 5-mg dose
example

a 10-nm-thick sample
Chicago and SI
example

a 5 mg dose
example

a 10 nm-thick sample

Unless your target journal’s guidelines specify a preference, choose one style and use it throughout the manuscript (i.e., be consistent). I prefer the APA style.