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The common number formatting convention uses a decimal point between the integer part and the fraction, and a comma between every three digits of the number:

1000000      -> 1,000,000
12345 + 1/5  -> 12,345.2

The . is referred to as Decimal Point. Is there an English word for the comma separating every three integer digits?

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Commas are used to separate large numbers into groups of three digits. Each group is called a period. – user41988 Apr 7 '13 at 7:39
Related: english.stackexchange.com/questions/96549/… – MετάEd Apr 7 '13 at 13:01
up vote 7 down vote accepted

It is often called the thousands separator or digit group separator.

For ease of reading, numbers with many digits before or after the decimal mark may be divided into groups using a delimiter, with the counting of groups starting from the decimal mark in both directions. This delimiter is usually called a "thousands separator", because the digits are usually in groups of three, that is, thousands. The most general name for this delimiter is "digit group separator", because thousands are not always the relevant group. For example, in various countries (e.g., China, India, and Japan), there have been traditional conventions of grouping by 2 or 4 digits.


Some countries use a period for the separator and a comma for the decimal mark.

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In maths lessons, we encouraged the use of spaces rather than commas: 'The problem with the point and the comma as either decimal mark or digit group separator is that, internationally, they have both often been used for both meanings, and their meaning is context-dependent ... which notational system is being used [?]). Therefore the space is recommended in the SI/ISO 31-0 standard, and the International Bureau of Weights and Measures states that "for numbers with many digits the digits may be divided into groups of three by a thin space, in order to facilitate reading."'(Wikipedia op cit) – Edwin Ashworth Apr 7 '13 at 7:53
In some languages the thousands are separated by a space. – Ilya Kogan Apr 7 '13 at 11:23
@EdwinAshworth Using spaces makes computer parsing problematic, because 123 456 is ambiguous. – Adam Matan Apr 7 '13 at 13:19
@donothingsuccessfully That's right, but most parsers, and regex splitters, would split the string by any whitespace. This include unicode spaces, newlines, nbsp and so on. – Adam Matan Apr 8 '13 at 8:08
Unfortunately in the real-world you will find numbers like 123,456.99, 123.456,99, 123 456.99, 123456.99 and 123456,99 so (even if you know the locale) you need to be extra careful with parsing plaintext. – Hugo Apr 8 '13 at 8:23

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