When should I write numbers as words?

Hey, I need some help. I don’t know when to write numbers as numerals (e.g., ‘3’) and when to write them as words (e.g., ‘three’).

Ok, let’s figure this out. It turns out that many organisations, such as the American Psychological Association (APA), have guidance for their members.  We can run through some of this.

Cool. What’s the first rule?

People over 30 years old shouldn’t say ‘cool’.

No, the first rule about when to write numbers as words.

Oh, ok.

If the number is less than 10, write it as a word. If it is 10 or more, use a numeral.

Example please.

I have seven cats and four dogs. This means I have 11 sets of mouths to feed each day.

And a lot of mess to clean up.


Are there any exceptions to this rule?

Oh, yes.

If you are using a number relating to a unit of measurement, or time, age, date, scores, etc, use numerals.

Example please.

The donkey was 6 years old, weighed 65 kg and ran at 8 mph. It took him 9 weeks to make the journey.

Ok, now you’ve raised a whole other set of problems (and I won’t even mention the Oxford comma issue). First, how and when do I use hyphens with numbers? Do I write ‘9 years old’ or ‘9-years-old’ or ‘9 years-old’. 

It depends.  Apparently, the rule is “when the age is an adjective that comes before the noun and modifies the noun, or when the age is a noun, hyphenate“.

What the hell does that mean?

If the age is a phrasal adjective describing someone or something, then hyphenate it.

That hasn’t made things much clearer. 

If you’re writing about an object (a person) and immediately before mentioning it you say it has the property of being such and such an age then shove in the hyphen. For example:

The 70-year-old kept telling me my grammar was bad.

Ok, but why shouldn’t I write “The seventy-year-old kept telling me my grammar was bad”

If it is a unit of time, use a numeral.

So do I always put those hyphens in when referring to age?

No, only when it is done to refer to an object. So, like this:

I asked the 70-year-old Steve how old he was and he told me he was 60 years old. 

Excellent. So my next question is do I use singular or plural abbreviations for things like weight. So do I write kg or kgs for example.

Apparently, the standard approach is to always use the singular, i.e., write 10 kg, not 10 kgs.

Rocking. Next question; do these rules change if I start a sentence with a number?

The guidance is to never start a sentence with a number. Re-write it somehow. If you must, then don’t use the numeral, use the word. So you would write:

Twenty people came to the party

What if 25 people came to the party and I want to start the sentence with the number. Do I write twenty five or twenty-five?

For numbers from 21 to 99, use hyphens (e.g., twenty-five). Once above that you don’t need extra hyphens (e.g., one hundred and twenty-five)

Great. Now you’ve given me the rules, can you unnecessarily complicate matters?

Always! So, we said that if the number is greater than 10 then write it as a numeral, unless you are starting your sentence with it. One alternative thing some people do is, if the number is greater than ten, but can be written out in two words, then do just that.

Example, please!

So, it seems ok to either write either:

He drank 21 bottles of beer that week


He drank twenty-one bottles of beer that week

In contrast, you would write:

He drank 365 bottles of beer a year

and not

He drank three hundred and sixty-five bottles of beer a year.

as the latter uses more than two words to write the number out with.

Similarly, you could write:

The dinosaurs had been dead for sixty million years

rather than

The dinosaurs had been dead for 60,000,000 years.

Hang on, didn’t you say if it was a unit of measurement, then you should always use a numeral? 

Yes, I did. But the APA state that “although the stylistic guidelines in the Publication Manual are meant to ensure consistency, they are not meant to replace your own reasoned judgment” and in my view the ‘sixty million’ version of this sentence looks nicer.

Grand. So, could you give me one sentence that illustrates the broad message of all this?


In 1984, the seventy-year-old Michael decided to send his four children, the youngest of whom was only 3 years old, to round up six sheep and 25 horses that had wandered 8 km away, whilst he sat down and drank 7 bottles of beer.

If I was 70 years old and had a 3-year-old child, I’d probably have to resort to drinking 7 bottles of beer a day too.


Hmm, I don’t like that you used the word ‘six’ to describe the number of sheep, but then switched to the numeral version of 25 to give the number of horses, it doesn’t look right.

So, in the 5th version of the APA Publication Manual said you should be consistent, but the 6th version of their manual says you can be inconsistent like this.

But if you want, by the two-word suggestion, you could also write 25 as twenty-five, and hence have this.

In 1984, the seventy-year-old Michael decided to send his four children, the youngest of whom was only 6-years-old, to round up six sheep and twenty-five horses that had wandered 8 km away, whilst he sat down and drank 7 bottles of beer.

Ok. One other thing, why are both of us writing a number, which is smaller than 10, as a numeral and not a word when we refer to ‘7 bottles of beer’?

I did this because, according to the Dictionary of Units of Measurement, a bottle is a unit of measurement. It should hence be written as a numeral.

I notice you used the word ‘because’ in that last sentence. Why didn’t you use the word ‘since’.

We are meant to use the word ‘because’ when we are explaining the reason for something. I was explaining the reason I wrote as I did and hence used this word. We use the word ‘since’ when we want to focus more on the result of what happened, rather than the reason that something happened.

Can I make one last observation.


You could do with a blog on grammar and using commas and grammar next.

I do not disagree with you there. I always pity the person who does my copy-editting.

Should that really be hyphenated?

Go away.


If you want to do a quiz to see if you have mastered all this – you can do one at the website below:



Note. This really is just a blog written to myself to help me figure out how to consistently write numbers in prose. If you have found yourself reading this though, and there are errors in the above, do please let me know!










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