Decimal separator and thousand separator

In English-speaking countries, a dot is used as a decimal separator. The European custom is to use a comma. A dot, comma, or space are used as thousand separators in different parts of the world. See the table for the practices of each country.

An example of the use of a decimal separator is, for example, 1.5. The part to the left of the comma represents the whole number. The part to the right of the comma represents a part of the whole number.

In the first centuries of the Common Era, Indian mathematicians developed a way of representing numbers based on the decimal system. The position of a digit in a number represents the ones, tens, hundreds, thousands, and so on. This Hindu-Arabic number system has also been expanded to parts smaller than a whole number, i.e. the decimal system. In such a decimal system, a symbol is needed to represent the difference between integers and decimal parts.

The Arabic mathematician Abu'l-Hasan al-Uqlidisi was the first to use the decimal part. This written source dates back to the 10th century.

Horizontal line as decimal separator in the Middle Ages

In the Middle Ages, it was customary to write a horizontal line above the last digit of an integer, i.e. the ones. For example, 1295 means 12.95. We can still see traces of this custom in the way prices are written, such as 12⁹⁵.

The Italian mathematician Giovanni Bianchini is said to have been the first person to use a dot as a decimal separator in his writing in the 1440s. Previously, the first person to use the dot was the German Christopher Clavius in his 1593 work Astrolabium. Bianchini's notations were taken up by Glen Van Brummelen in 2024 in his article in Historia Mathematica.

As printing press became more widespread, the use of dot and comma was preferred. They were easier to use in printing press as separate characters.

Comma established in France, dot in England

In France, a dot was used as a kind of decimal separator in connection with Roman numerals. For example, the Roman numeral MCCCLXXVIII (1378) was presented as M.CCC.LXX.VIII for clarity. Since the dot was already reserved for this use, the comma was chosen as the decimal separator. This practice began to be followed in many other countries as well.

In English-speaking countries, the dot became the decimal separator.

The use of a comma or dot as a decimal separator is standardized in the ISO standard ISO 80000. So, either one can be used. However, practices vary by country and language.

A thousand separator can be used to make it easier to interpret numbers

A thousand separator is also used for large numbers. In some countries the thousand separator is a space, in some a comma, and in some a dot. The thousand separator is not required to be used, but it usually makes it easier to interpret large numbers.

Table: decimal separator and thousand separators in different countries

The following is a table that describes the situation in different countries regarding the decimal separator and thousand separator. The ␣ in the table means a space.

For example, in Switzerland and Estonia, the decimal separator is a comma, but in connection with currencies, a dot is used.

The comma is used as a decimal separator in most of Europe, Latin America, parts of Africa, Russia, Indonesia and Vietnam.

The dot is used as a decimal separator in English-speaking countries, Asia and parts of Africa. Examples of Asian countries include China, Japan, Korea, Thailand, Pakistan and the Philippines.

In India, a million is 10,00,000

In India, the decimal separator is a dot, but there is a special feature associated with the use of the thousand separator. The first thousand separator normally separates three digits, but the following separators only separate two digits. The thousand separator is a comma. Or, well, it is no longer a thousand separator. So, a million in India is 10,00,000.

Considering the possibility of using a dot, comma, and space as thousand separators, it can be stated that the interpreter of numbers in different countries has all reasons to be careful. Furthermore, even in those countries where the decimal separator should be a comma, a dot may be used as the decimal separator as a result of the English language or different software requirements. The use of a thousand separator can add to this confusion.

Author:

Arkikoodi

Sources and additional information:

Wikipedia: Hindu–Arabic numeral system

Wikipedia: Decimal separator

Wikipedia: Abu'l-Hasan al-Uqlidisi

Historia Mathematica: Decimal fractional numeration and the decimal point in 15th-century Italy

Phys.org: Use of decimal point is 1.5 centuries older than historians thought

Wikipedia: Giovanni Bianchini

Wikipedia: ISO 80000

Published: 16.9.2025

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