To write out numbers or not

Numbers appear in almost every thesis, whether you do extensive statistical analysis or not. When should you write out numbers, and when shouldn’t you? Here, we explain the rules for both Dutch and English-language theses.

The answer to the question is not so simple, and not always the same.. The answer depends on the context and the number in question. The most important rules are explained below.

Basic rule: write out round numbers and numbers under twenty

In Dutch, write out round numbers and numbers below twenty. You do not have to do so for non-round numbers above twentys.

Here are some correct examples:

• "Research by Jansen and Pieters among 13 students shows that..."

• "The four interviewees tell us that..."

• "There were 235 respondents."

• "At least 50 people attended the demonstration."

Exact values

There is an exception to this rule for exact values. When discussing exact values, such as amounts or kilograms, you do not write out the numbers as words. 

The same applies if you discuss research results or a research design, and share several figures in one paragraph. In this case, you don't write out all the numbers like you would if they stood alone. This is because it can get messy to be spelling some out and not others. Therefore, stick to putting the numbers in figures instead.

Correct examples of these rules include:

• "The estimated turnover is €200,850."

• "The poachers captured a total of 500 kilos of fur."  

• "The survey of 26 students shows that 5 students suffer from fear of failure. From this group, 3 students indicated that they have it to a severe degree."

Percentages

You never write out percentages. You always keep them as numbers. In principle, you round off percentages to one decimal place. If it is a round percentage, you simply make it 14%, 26%, etc. and no decimal place is needed.

A correct example is "In this survey, 17% of respondents indicated that...".

Wrong would be : "In this survey, seventeen percent of respondents indicated that..."

Chapter numbers

There is a separate category of numbers to consider: chapter and paragraph numbers. You often put a number above a chapter or paragraph (such as 2 or 2.1). These chapter numbers are never written out in words, even if you refer to them in the text. 

So not: "I will discuss this in chapter two."

Instead say: "I discuss this in Chapter 2."

In short: the basic rule is that you write out round numbers and numbers under twenty. Different rules apply in different situations, for example...

• ...when it comes to exact values (such as years, amounts or measurements);

• ...When it comes to ages;

• ...If you refer to chapter, paragraph, page or table numbers in the text;

• ...if several numbers are written as numbers in the same paragraph (e.g. in the method chapter and in the results chapter). 

Note, however, that sentences should never start with a number. So this sentence is incorrect:

"132 respondents completed the survey with a total of 15 questions."

Rephrase such a sentence in a way that the number is no longer at the front of the sentence. For example, you can turn that exampleinto the following:

"The survey, with a total of 15 questions, was completed by 132 respondents."

These are the guidelines for the Dutch language. What about according to APA, the most commonly used style of source citation for theses? According to the latest APA guidelines, you should only write out round numbers below ten (instead of round numbers and numbers below twenty). So according to that guideline, you also write "12" instead of "twelve."

If necessary, ask your thesis supervisor which guidelines you should follow for numbers. In any case, the exceptions to the rule for writing out numbers listed above still apply, including APA.

Besides the dilemma of when to write out numbers, there are other important things to consider when using numbers in your thesis. The most important one? Always put a full stop before thousands. In other words, put a full stop before every three digits. 

Correct is thus:

• "This mistake cost the government €250.000," he said.

• "In the survey, 2.832 respondents participated."

• "In total, as many as 1.500.000 kilos of fish were caught."

Decimals always come after a comma in Dutch. So it is "€250,50" and "45,6%" and not "€250.50" and "45.6%".

If you are writing your thesis in English, the guidelines are different than for a Dutch thesis. When should and shouldn’t you write out numbers? In an English thesis,the APA rules for writing out numbers usually apply. You can assume that you should write out numbers under ten and round numbers. Other numbers stay written in numbers. However, the above exceptions still apply (such as not writing out paragraph numbers). 

There is one more thing to bear in mind. In English, the use of commas and full stops in numbers is exactly the opposite of how we use them in Dutch. For thousands, you put a comma before every three digits instead of a full stop. Before decimals, on the other hand, you put a full stop.

Correct is thus: 

• "This book is being sold for €16.99". (In Dutch, you would write this as "€16,99".)

• "Almost 1,500,000 students went to college this year." (In Dutch, you would write "1.500.000 students" here).

When to write out numbers or not is just one more of the dilemmas you need to be aware of while writing your thesis. Want to make sure your thesis is free of spelling, language and typing mistakes? Let our experienced editors check your thesis for you. They will filter out misspelled numbers and all kinds of other errors you may have missed on your own.