An Overview of Spanish Numbers:

We use numbers to count and indicate how many nouns are being described. The main challenges in writing numbers involve the forms and spelling.

Let's first consider the words Spanish uses for cardinal numbers:

• the numbers from dieciséis to veintinueve are written as one word; note the accents on dieciséis, veintiún, veintidós, veintitrés, and veintiséis
• write veintiún without an "o" on the end and with an accent when it occurs before a masculine noun; write veintiuna before a feminine noun, e.g.: Hay veintiún libros y veintiuna sillas en el salón. Use veintiuno when the masculine noun does not directly follow the number, e.g.: ¿Cuántos niños hay? Hay veintiuno.
• take care to learn which numbers are written with an "ie" letter sequence and which are written with an "ei" sequence as this is one of the most common student spelling/pronunciation errors
• be careful of the distinction between 60 sesenta and 70 setenta that only differ by one letter (to help you remember which is which, note that sesenta has an "s" like seis and setenta has a "t" like siete)
• in a sentence, write numbers below 99 and numbers that can be written in one word with letters, e.g.: uno, dos ... ocho, nueve, diez, dieciséis, veintiocho, treinta, sesenta y cuatro, noventa y nueve, doscientos
• For the hundreds, they will change gender depending on the gender of the noun that follows or the gender of the noun that the number refers to, e.g.: Hay trescientas personas en la reunión. ¿Cuántas mujeres hay? Hay doscientas.
• do NOT use un before cien or mil
• when writing larger digits, use a period NOT a comma to separate thousands, e.g.: 1.000.000, and use a comma for the decimal marker, e.g.: 8,75.
• use de after un millón if a noun follows, e.g.: un millón de personas.

Ordinal numbers

Ordinal numbers allow us to establish an order or rank, e.g.: "first", "second", "third" (primero/a/primer, segundo/a, tercero/a/tercer). The main ordinals in Spanish are presented in the following table:

Ordinal numbers can also appear in the plural to match the number of the noun they modify, e.g.: Ellas eran las quintas en llegar.

Ordinal numbers also usually go in front of the noun they modify, e.g.: Es el tercer presidente del club. When the forms primero and tercero appear directly in front of a masculine noun they drop their final "o" as seen in the previous example.

Abbreviated Ordinal Numbers

It is common in Spanish to abbreviate ordinal numbers. To abbreviate ordinals, use a decimal after the number and then superscript letters depending on which ordinal you are using. Use "er" for primer and tercer only, e.g.:

• primer >  1.^er
• tercer >  3.^er

Use a superscript degree sign º for masculine ordinal numbers and a superscript letter ª for feminine ordinal numbers, e.g.:

• primero/a > 1.º/1.ª
• segundo/a > 2.º/2.ª
• tercero/a > 3.º/3.ª

• in dates, don't use an ordinal other than primero, e.g.: el 2 de septiembre and NOT el 2.º de septiembre (unless you are referring to a succession of Septembers over multiple years!)

• adjectives
• determiners
• numbers