It can be difficult to know how to write numbers in academic writing (e.g. five or 5, 1 million or 1,000,000). This section gives some guidelines on when to use words to write numbers, and when to use numerals. There are also some exceptions to the rule which are considered, i.e. times when you might expect to use words but should instead use numerals. There is also a checklist at the end, that you can use to check the use of numbers in your own writing.

When to use words

In general, words should be used for zero to ten, and numerals used from 11 onwards. The same rule should be applied to ordinal numbers, i.e. use words for first, second up to tenth, and numbers plus 'th' (or 'st') from 11th onwards. However, it is always best to check what the accepted practice is at your university (or in your department/on your course), and remember that some common referencing systems have their own, different requirements, as follows.

• MLA. Use words if the number can be written using one or two words (e.g. three, twenty-seven).
• APA. Use words for numbers zero to nine.
• Chicago. Use words for numbers zero to one hundred.

Before looking at when to use numerals (which is almost all other situations, see next), it is useful to look at important exceptions.

(1) When the number begins a sentence, you should use words, whatever the size of the number (though if possible, rewrite the sentence so the number is not at the beginning).

• Fifty respondents agreed with the statement.
• There were 50 respondents who agreed with the statement. [rewritten sentence]

• 50 respondents agreed with the statement.

(2) When expressing part of a very large round number, e.g. million, billion, you should use words for that large number part (it is common to use abbreviations m for million and bn billion).

• The population of the earth is now in excess of 7 billion people.
• The population of the earth is now in excess of 7bn people.

• The population of the earth is now in excess of 7,000,000,000 people.

• The population of the UK is approximately 70 million.

• The population of the UK is approximately 70,000,000.

Conversely, numerals should be used rather than words, whatever the size of the number, when large and small numbers are combined, since this makes comparisons easier.

• There were 2 respondents in the first category, and 22 in the second.

• There were two respondents in the first category, and 22 in the second.

When to use numerals

Numerals are used for almost all other situations. These include the following.

• Measurements (e.g. 6 kg, 3 cm, 10 min, 2 hr, 3 days, 6 years, 5 decades)
• Currency (e.g. $10, £50, £60 billion)
• Statistical data, including survey data (e.g. A survey of participants revealed that 4 out of 5 students worked.)
• Mathematical functions (e.g. v² = u² + 2as)
• Decimals (e.g. 2.5, 4.54)
• Percentages (e.g. 75%)
• Ratios (e.g. 3:1)
• Percentiles/quartiles (e.g. the 95th percentile, the 1st quartile)
• Times (e.g. 12.30 a.m., 6 p.m., 16:00)
• Dates (e.g. Wednesday 25 December 2019)
• Scores/points on a scale (e.g. This item scored 5 on a 9-point scale)

Other important points

The following are a few other points to remember when using numbers.

• Consistency. You should be consistent in how you write numbers; for example, if write a figure like 7bn in one place, do not write a figure like 5 billion in another.
• Use of commas. When giving numerals of 1,000 or larger, use commas for each thousand, e.g. 5,500, 8,326,500.
• Use of hyphens. When displaying a range, use a hyphen, with no space, e.g. 30%–50%
• Expressing fractions. Fractions can be written either as numerals e.g. 2/3 or words e.g. two-thirds. If using words, use a hyphen.

References

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Checklist

Below is a checklist for using numbers in academic writing. Use it to check your writing, or as a peer to help.

Item	OK?	Comment
Words have been used for numbers between one and ten, and numerals for numbers 11 and above (unless there are different requirements e.g. MLA, APA, Chicago).
Numbers (written as numerals) are not used to start a sentence.
Very large round numbers are expressed using million/billion.
If small (ten or less) and large (11 or more) numbers are used together, numerals are used throughout.
Numerals have been used for measurements, currency, statistics, functions, decimals, percentages, ratios, percentiles, times, dates and scores.