Cardinal numbers are the usual numbers we use to count. Following are the numbers from 1-20.
* Uno becomes un when it precedes a masculine singular noun (un dólar). It becomes una when it precedes a feminine singular noun (una cosa).
* *An alternate for these four forms is diez y seis, diez y siete, diez y ocho, and diez y nueve. See below for how the conjunction y is used to form combined numbers.
The cardinal numbers twenty through one hundred by tens are as follow:
* Cien occurs whenever it precedes a noun. Otherwise it remains ciento. (Cien casas. Ciento cincuenta perros.) Also, one should remember that, although in English one says "a hundred," in Spanish the indefinite article is not used, i.e. "Tengo cien cosas que hacer."
The cardinal numbers twenty-one through ninety-nine follow this pattern:
* The numbers 21-29 have two possible forms. 31 and above do not have a combined form.
* *The number 21 has three possible forms, depending on the noun it modifies: veintiuno (by itself), veintiún caballos, veintiuna rosas.
Counting by hundreds, from two hundred to one thousand, we have the following numbers (note both maculine and feminine forms):
* Notice that mil has only one form for both masculine and feminine, while the other numbers have both forms. Also, one should remember that, although in English one says "a thousand," in Spanish the indefinite article is not used, i.e. "Tengo mil cosas que hacer."
The next large numerical division is the word "million." The
word is used as a noun, however, not an adjective. For this reason
the number un (or dos, tres, etc.) precedes the word.
In addition, the preposition de follows:
Above the number fifteen, combinations of tens and units require the use of the conjunction y. That is: veinte y dos (veintidós), treinta y ocho, and ochenta y siete. The conjunction does not, however, come between all numbers; it usually separates the tens from the units.
* Note that where English uses a comma before the decimal point, Spanish uses a period, and conversely where English uses a period for the decimal point, Spanish uses a comma.
Ordinal numbers stress numerical sequence, i.e. first, second, third, twentieth, hundredth, etc. The most commonly used ordinal numbers (in the masculine and feminine forms) are:
* As happens to bueno and malo, when primero and tercero precede a masculine singular noun they lose their -o: El primer / tercer mes del año.
Ordinal numbers in Spanish are commonly used through "tenth"
(décimo), but beyond that the cardinal numbers are
more frequently used.
Although both the cardinal and the ordinal numbers precede the
noun modified, see placement
of adjectives for exceptions.