How to Format Numbers in Your Manuscript

In academic publishing, there is a large amount of conflicting information when it comes to style. Big journals often have different preferences, especially when it comes to formatting numbers. Nonetheless, is most important to adopt a consistent style throughout your paper. Here, we present a basic guide on formatting numbers to help get your paper in a publishable state.

Spacing

In academic writing, numbers are commonly used before units and mathematical operators. Although it is common in casual writing to use no space between a number and unit (e.g., 10ml), most published writing uses a space between the number and unit. There are a few exceptions, such as temperatures (e.g., °C) and percentages (%).

Example: Then, 3 g of the material was immersed in the solution.

Example: The samples were stored at −80°C.

This rule applies to other functions as well, such as ±.

Example: 2.43 ± 0.19

Overall, using a space between numbers and units makes the text more readable by creating more white space in the text. Unless your target journal specifically avoids this practice, we suggest employing it.

Numbers versus words

One of the biggest formatting concerns is knowing when to spell out numbers (e.g., seven) over using the numeral itself (e.g., 7). This varies widely between style guides and journals, but most guidelines agree on a few points. First, the most important rule is that numbers below 10 should be spelled out in regular text.

Example: After the two samples were washed with PBS, they were each divided into four equal parts and placed into separate flasks.2.43 ± 0.19

There are many exceptions to this rule, and we will cover some of them here. If a number comes before a unit or is used in a mathematical operation, then the numeral should be used regardless of the value.

Example: Only six of the patients experienced pain in their arms.

Example: Only 6% of the patients experienced pain in their arms.

If a number would start a sentence, then it should be written out.

Example: Fifty-eight cases were included in this study.

However, one should refrain starting a sentence with a number altogether. Thus, rewriting may be a better option in many instances. The above sentence could be rewritten as follows.

Example: A total of 58 cases were included in this study.

If numbers appear in a list, they should all be written in numerical form if one of them is 10 or above. Consistency within the same list helps when reading the sentence.

Example: Plants 3, 8, 11, and 22 were adversely affected under salt stress.

Use numbers when referring to units of time, even if those units of time are fully spelled out. Common expressions of time include days, weeks, months, and years

Example: We monitored the materials over the course of 2 months.

Example: Within 3 weeks, the temperature rose an average of 5°C.

Numbers in tables

Tables often contain data that are reduced to a numerical form. As a rule, use numbers instead of words in all cases. Be sure that the same number of significant figures is used throughout the same categories in the table. It can be difficult for readers to interpret different numbers of significant figures and a mixture of words and numbers, so consistency is key to making the table look clean. An example table is provided below. Single-digit numbers are given in numerical form, and the percentages are rounded to the third value after the decimal.

Numbers in tables

Separators

In the United States, commas are used as the thousands separator. Other countries and institutions have different conventions and may use either period or spaces. Journals usually default to the standard presented below, with a period as the decimal separator and commas as the thousands separator.

Example: 1,250,695,200.13

While some of the above examples may not be universally applied by all journals, using a consistent style for numbers in your manuscript’s text will increase its chances of being favorably received by journal editors and reviewers.