Pronouncing the Decimal Comma

It's pretty much as you might have guessed: In casual usage, you can pretty much follow the convention of English, except that instead of saying something like "three point two five," you can use the Spanish word for "comma," which is coma: "tres coma dos cinco."

International Standard of Using Decimal Commas

The international standard is to use a comma in numerals where English would use a decimal point. But the Royal Spanish Academy does recognize use of the decimal point (or period) when used by Spanish-speaking people in English-language countries, and in those parts of Latin America (such as Mexico) where English-language influence has led to use of the decimal point. In those areas, 3.25 can be pronounced as "tres punto dos cinco."

A more formal way of pronouncing the same number, and one that doesn't depend on how it is written, is "tres enteros y veinticinco centésimos" (the y is often omitted), the equivalent of "three and twenty-five hundredths." (Entero is used to refer to whole numbers.) You'll hear some speakers use céntimos instead of centésimos to refer to hundredths in this context.

The number could be rounded down to 3,2 (or 3.2 in parts of Latin America), which would be "tres coma dos" or "tres enteros y dos décimos" (three and two-tenths).