Commas and Periods (Full Stops) with Numbers (UK and US)

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The Quick Answer
Commas can be used with large numbers to assist the reader. They are placed every three decimal places to the left of the decimal point, which is marked with a period (full stop). For example:
  • 123,456.789
Be aware that many other countries use the reverse formatting, i.e., they use periods (full stops) to mark out every three decimal places and a comma for the decimal point. For example:
  • 123.456,789
  • (This would be correct in many non-English-speaking countries, such as Germany and France.)
commas and periods (full stops) in numbers UK/US and Europe

Using Commas with Numbers

In countries like the US, UK, and China, commas are used with large numbers to make them easier to read. A comma is placed every 3 decimal places for numbers larger than 999. The decimal point is shown with a period (full stop). For example:
  • 1,234
  • 23,566
  • 1,234,967
  • 8,000
  • 8,000.01
  • 8,000.0123456

No Commas to the Right of the Decimal Point

The most common convention is not to use commas to the right of the decimal point. For example:
  • 4,567.123456
  • 4,567.123,456
  • (This would be considered unusual.)

Other Conventions for Writing Numbers

The use of commas and periods in numbers is not consistent across the world. Below are the most common conventions:
  • 4,567.1
  • (United Kingdom, United States, China)
  • 4.567,1
  • (This convention is used in most of Europe. It is the convention used by most countries.)
  • 4 567,1 and 4 567.1
  • (The practice of using a space to separate the 1000s is also common.)

Do Not Add Commas to Serial or Reference Numbers

Do not put your own commas in serial numbers, reference numbers, or 4-figure years. For example:
  • According to the document with reference number 912345, serial number 1654880 was destroyed in 1984.
When years are not in the 4-figure format, it is possible to use commas. For example:
  • The film is set in 10,000 BC.
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See Also

Using commas (a summary) Try our test on using commas Numbers as compound adjectives How to write numbers in full Starting sentences with numbers Commas after a sentence introductions Commas after a transitional phrase Commas after interjections (yes, no, indeed) Commas before conjunctions (and, or, but) Commas for parenthesis Commas in lists Commas with a long subject Commas with quotation (speech) marks Commas with the vocative case Commas with Dear, Hello, and Hi