Using Numbers And Unit Symbols In Measurements - Ibiblio

Decimal Points and Markers: In English-speaking countries (except South Africa), in Mexico and in most Asian countries the period (.) is used as the decimal marker (decimal point) to separate the whole number and fractional portions of a number. In continental Europe and most South American countries the decimal marker is the comma (,). The International System (SI) allows either the period or the comma to be used; the Dictionary uses the period. Wikipedia's decimal separator article has a lists of countries using each marker.

Digit grouping: Since the comma is often used as a decimal marker, it should not be used to separate groups of digits. The SI recommends that numbers having many digits be represented as groups of three digits separated by narrow spaces, like this: 2 675 491. The Dictionary observes this convention. The SI also allows large numbers to be written without any grouping, as in 2675491, but it does not allow the use of commas or any other grouping marks other than narrow spaces.

Large numbers: How many is a billion? In America, the word "billion" means the number 1 000 000 000, or 109. In Britain, this number is (or was) traditionally called "one milliard" or "one thousand million," and "billion" means the number 1 000 000 000 000 or 1012, which is what Americans call a "trillion." Most other European languages have similar expressions, such as mil millones for 109 and billón for 1012 in Spanish.

The Dictionary uses the American definitions for large number names. Although the General Conference on Weights and Measures endorsed the European names in 1948, the American definitions seem to be gaining ground in Britain and perhaps elsewhere. See Names for Large Numbers for more on this question.

There's always interest, especially among school children, in knowing the names of still larger numbers: quadrillions, quintillions, etc. These names are also listed in on the Names for Large Numbers page.