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

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Commas in Numbers

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.)

Using Commas in Numbers (US, UK, and China)

In the US, UK, and China, 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.)

The table below shows how numbers are written in US, UK, and China:

billions

, (comma)

hundred millions

ten millions

millions

, (comma)

hundred thousands

ten thousands

thousands

, (comma)

hundreds

tens

units

. (point)

tenths

hundredths

thousandths

ten thousandths

hundred thousandths

millionths

NB: Historically, a billion in the UK was a million million (1,000,000,000,000). However, in 1974, Prime Minister Harold Wilson brought the term "billion" into conformity with wider international usage, making a "billion" equal to a thousand million (1,000,000,000).

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.)

The table below shows how numbers are written in most European countries:

billions

. (point)

hundred millions

ten millions

millions

. (point)

hundred thousands

ten thousands

thousands

. (point)

hundreds

tens

units

, (comma)

tenths

hundredths

thousandths

ten thousandths

hundred thousandths

millionths

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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