Grammar GuideCommaWhen should I use a comma to separate numbers?

When should I use a comma to separate numbers?

When should I use a comma to separate numbers?

In English, we use commas in numbers greater than 999 to split the number and make it clearer. We use a comma every third digit from the right.

  • More than 50,000 people turned up to protest.

The comma every third digit is sometimes known as a “thousands-separator.” Make sure you don’t include a space on either side of this comma.

Correct:

  • We will walk 10,000 miles.

Incorrect:

  • We will walk 10000 miles.
  • We will walk 10, 000 miles.
  • We will walk 10 , 000 miles.
  • We will walk 10 ,000 miles.

When a number uses a decimal point, we never place commas to the right of the decimal point. Some people like to use thin spaces going from left to right instead.

Correct:

  • The value of Pi is 3.14159 to five decimal places.
  • The value of Pi is 3.14 159 to five decimal places.

Incorrect:

  • The value of Pi is 3.141,59 to five decimal places.
  • The value of Pi is 3.14,159 to five decimal places.

Numbers that are not amounts, such as phone numbers, house numbers, and years do not usually have commas.

It can get confusing as many other countries (such as Spain) use commas in numbers instead of a decimal point, e.g. 100,01 instead of 100.01. In these cases, you might see a period used instead of commas or a space, e.g. 1.000,01 or 1 000,01 instead of 1,000.01. But for English-speaking countries, follow the rules above.

Common Questions about Comma

Should an introductory phrase be followed by a comma?When should you use a comma before a coordinating conjunction?How do I add commas to a number for clarity?What is a comma splice and how do you fix it?Do I need a comma after a subordinate clause?Do I need a comma after a participle phrase?How should I use commas with 'not only... but also'?Should I use a comma before a subordinate conjunction?Do you need a comma in a compound predicate? When is a comma unnecessary?Why should you put comma after prepositional phrases?Do I need a comma when I omit a word for stylistic reasons?Do you need a comma after an adverbial infinitive phrase?Should I use a comma at the end of a quotation, before the closing quotation mark?Should I use a comma before an opening quotation mark?Should I use a comma before "which"?Should I use a comma before and after an appositive?Should I use a comma before "not"?Do I need to use a comma with list items?How do I use commas with parenthetical elements?Should I use a comma between a city and a country/a city and a state?Should I use a comma before and after vocative?Do you need a comma to separate the day from the month, and the date from the year?Do you need a comma before or after "too"?Should I use a comma before or after “please” in a sentence?Is it grammatically correct to put a comma before "and"?Is it grammatically correct to put a comma before "then"?Should I use a comma after an introductory adverb like "apparently"?Should I use a comma after a time phrase such as "in the meantime"?How should I use a comma with a subordinate clause?Should you use a comma before "whereas" and "although"?Should you use a comma before "while"?Should you have a comma before "because"?Should I use a comma before "for"?Should I use a comma before "since"?Should I use a comma between two adjectives?Should I use a comma with a participle or gerund phrase?