When using numbers in academic writing you need to decide if it’s more appropriate to use a numeral (e.g. 9) or to write the number in words (e.g. nine). It’s worth checking to see if your department has specific advice on this matter, because individual approaches do vary. In the absence of specific advice, here is some general guidance on the matter:
- Numbers up to nine should always be written in words, anything higher than nine can be written in numerals. Alternatively, some guides suggest that if you can write the number in two words or fewer then use words rather than numerals. If you are going to take this approach then you should include a hyphen when writing numbers with two words, e.g. twenty-seven.
- For larger numbers, it is acceptable to use either numerals or words depending on context (e.g. a thousand people/1,000 people), but you should always use numerals in technical writing, e.g. 200,000 km. For less precise larger numbers, the written form is better (e.g. several thousand).
Measurements and decimals/fractions
- Use numerals for units of measurement or time, e.g. 500 km, 10 minutes.
- Always use numerals for decimals and fractions (e.g. 0.5 cm) unless the figures are vague (e.g. around half of the population).
- Units of measurement that modify a noun should be hyphenated, e.g. a 3-year-old child.
Dates, money and time
- Always use numerals for dates, e.g Monday 4 April, 2016.
- Use numerals for money (e.g. His pocket money was exactly $1.00 per week) unless the amounts are vague (e.g. He earned well over a million last year).
- Use numerals for indicating the precise time (e.g. 08:00), or words if the times indicated are vague (e.g. around eight o’clock).
If you need to combine two numbers that run together then use words for the shorter number and numerals for the longer number, e.g. a tower of 1000 two-dollar pieces.
Starting sentences with numbers
Avoid starting a sentence with a numeral. Either write the number in words or rearrange your sentence. For example, “Three hundred and sixty-five days make one year” could become “There are 365 days in a year”. If you start a sentence with a year, write “The year” first e.g. “The year 1066 saw one of the most famous battles in English history”.
(Source: The University of Hull)