Punctuation Tips: Using Commas in Numbers
  • 4-minute read
  • 14th August 2021

Punctuation Tips: Using Commas in Numbers

While commas are often used to separate words, phrases, or clauses in a sentence, they are also used in large numbers. Check out our guide below to learn how and when to use commas in numbers in your writing.

Thousands Separator Commas

In English, you can use commas in numbers of four digits or longer (i.e., numbers above 999) after every third digit from the right. These “thousands separators” make it easier to read long numbers since we can see where the different groups of digits fall at a glance. Compare the following, for example:

Their video got more than 50,000,000 views.

Their video got more than 50000000 views.

In the first case, we can clearly see that the number is 50 million, as the commas help us to see the groups of zeroes. By comparison, in the second one, we might need to count the zeroes to be sure that it isn’t five million or 500 million instead.

This only counts for numbers larger than one, though! As such, thousands separators are not required for numbers that appear after a decimal point:

The number came to 1,287.432091.

The number came to 1,287.432,091.

Thousands separators aren’t compulsory, though. If you prefer to write fifty-thousand as “50000,” that’s fine! However, as shown above, adding a separator in a number like this can make it easier to read, and many style guides will suggest using commas like this (so make sure to check your style guide if you’re using one).

Thousands Separators in Other Languages

Most English-speaking countries, including the US, Australia, and the UK, use commas to separate groups of thousands and a period as a decimal separator (as shown in the examples above). However, other countries flip this around, using a period between groups of thousands and a comma as a decimal point. For example, a native Spanish speaker might punctuate the numbers above as follows:

Their video got more than 50.000.000 views.

The number came to 1.287,432091.

This ambiguity is why some organizations use a space instead of punctuation to indicate groups of thousands, with the comma only used as a decimal separator.

If writing for an audience that includes people in countries with different rules for punctuating numbers, then, we might write the numbers above as follows:

Their video got more than 50 000 000 views.

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The number came to 1 287,432091.

This is only necessary when writing for an international audience, though. If all of your readers are English speakers, we suggest sticking to using commas as thousands separators and a period as a decimal point.

Commas in Years

Four-digit years are an important exception to the rule about thousands separators. Notably, you never need a comma in a year made up of four digits:

William Shakespeare was born in 1564.

William Shakespeare was born in 1,564.

However, you can use a comma in years of more than four figures. For instance:

Roland Emmerich’s film is set in 10,000 BC.

This will only apply to years in the distant past or future, though.

When Not to Use Commas in Numbers

Not all long numbers require decimal separators! Notably, long sequences of numbers that work to identify rather than quantify something, such as telephone and serial numbers, never use commas to separate groups of digits.

For instance, while you might add hyphens between groups of digits in a phone number to make it easier to read, you would not need to add commas:

To find out more, call 202-555-0192.

To find out more, call 2,025,550,192.

For numbers like these, then, there is no need to add thousands separators.

Proofreading for Punctuation

Since there are many rules to follow, proofreading is a great way to make sure your writing is always clear and easy to read. If you’d like more advice on your comma use or with any other punctuation, try our proofreading services for free today!

Comments (4)
Marsha Mac
17th March 2022 at 22:26
What about when writing series of numbers such as this: about 200,000 chimpanzees, 20,000 bonobos, 100,000 gorillas, and 100,000 orangutans remain. Should semi-colons be used after each word before the numerals?
    Proofed
    18th March 2022 at 09:36
    Hi, Marsha. You could use semicolons between the numbers if you were worried that the sentence would be difficult to read with just commas, but it looks fine to me (the fact the thousand separators aren't spaced whereas the list commas have a space after them means they're clearly visually different as it stands).
Alexandra
27th October 2022 at 16:25
Hello! What about using commas as separators in entities like 2200W or 3000V? It seems to be fine not to use comma in these cases, but I can't explain why
    Proofed
    28th October 2022 at 16:41
    Hi, Alexandra! It’s difficult to find a definite answer to this but the UK Metric Association recommends that a separator is only used for numbers of more than four digits (though a space is preferred rather than a comma), so this might be why you don’t see a comma in these cases. As separators are a matter of preference anyway, it best just to make sure any usage is consistent in your document or check what your style guide (if there is one) advises.

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