How to Write Numbers in Spanish

Writing Cardinal Numbers

Memorize unique names of numbers. The first 15 numbers in Spanish have unique names that you'll need to learn. After those, the numbers come in combinations, so you can form more numbers by combining the names of the ones you already know. The words for the first 15 numbers in Spanish are uno (1), dos (2), tres (3), cuatro (4), cinco (5), seis (6), siete (7), ocho (8), nueve (9), diez (10), once (11), doce (12), trece (13), catorce (14), and quince (15).

Learn to count by tens. The tens in Spanish are unique words as well. Recognize the pattern that most of these are more or less a combination of the word for the first digit and the suffix -enta. For example, cuarenta is a combination of cuatro (4) and the suffix -enta, with the "t" removed as well. To write numbers through 99, all you need are the tens and the second digit, separated by the word y. For example, 34 would be "treinta y cuatro," which literally means "30 and 4."

Use -cientos for hundreds. To create the full word for a number in the hundreds, you simply add the word for the other digits to ciento or cientos. For example, two hundred is doscientos. The only exception is the word for the number 500, which is quinientos.

Connect tens and ones with the word "y" (and). When writing out large numbers in Spanish, you need an y between the second and third digit of each grouping of three digits. This is the case regardless of how many groupings there are. For example, if you wanted to write the number "999,999" in Spanish you would write the words as "novecientos noventa y nueve mil novecientos noventa y nueve." The literal translation of this into English is "nine hundred ninety and nine thousand, nine hundred ninety and nine."

Learn the word "mil." In Spanish, you use "mil" for "thousand." If you're writing about something that is exactly 1,000, you should only write "mil," not "un mil." The plural form of "mil" is "miles." There is an exception if you're writing a check in Spanish and the amount begins with "one thousand." Then you usually should write "un mil" rather than "mil" to prevent someone from altering the check – even though this is technically incorrect.

Use the word "millón" for a single million or "millones" for several million. Write the words just as you would in English, by writing first the number of millions there are, and then writing the rest of the numbers.

Keep in mind that a billion in Spanish is not the same quantity as in English. In Spanish, extremely big numbers in the billions and trillions are counted differently than they are in English. If you fail to recognize this, you could make a significant error when writing numbers in Spanish. In Spanish, the number you would call "one billion" in English is called "mil millones," or "thousand million." The Spanish word "billón" is equivalent to the number you would call "one trillion" in English.

Shorten the words ciento, uno, and veintiuno. In Spanish, if you're speaking of exactly 100, you must shorten ciento to cien. The numerals uno and veintiuno also are shortened to un and veintiún if they are immediately before another number, a noun, or an adjective. For example, if you were talking about one dog, you would write "un perro." When you're using the feminine forms of these numbers, however, they are not shortened. For example, if you were writing about one ball, you would write "una pelota."

Use decimal points and commas correctly in numerals. One of the biggest differences between written numbers in Spanish and written numbers in English is the use of decimal points and commas. When you write numbers in Spanish, separate thousands with a decimal point – not with a comma as you would in English. For example, you would write "126,342" as "126.342" in Spanish. Decimals, on the other hand, are written using a comma. For example, if you wanted to write pi in Spanish, you would write "3,14159265359."

Separate thousands with a white space. While decimals are still acceptable to use when separating thousands as you write numbers in Spanish, it also is acceptable to simply use a space. This method has become more common as a way to separate thousands because it keeps the decimal point from being confused with the comma.

Make number words agree with the things they describe. If a number word describes a feminine noun, you should write it so that it ends in -a rather than -o. Unless you're referring to exactly one thing, the noun also must be pluralized. For example, if you were referring to 20 houses, in Spanish you would write "veintiuna casas." Keep in mind that in Spanish, anything that isn't exactly one must be pluralized. For example, on an invoice or spreadsheet, you would pluralize the noun even if the quantity listed was "1,00" (expressed in English as 1.00).

Use cardinal numbers with dates. In English, you might write "April first" in a paragraph about April Fool's Day. However, in Spanish, you would write "1 abril," putting the day first and using the cardinal number rather than the ordinal.

Writing Ordinals and Multiples

Use ordinals to put things in order. Cardinal numbers are used to count things, or describe the number of things there are. Ordinal numbers, on the other hand, describe the placement of something in an ordered list, such as the placement of runners who finished a race. As in English, the lowest ordinals, such as primero (first), and segundo (second), typically are used the most.

Make ordinals agree with the thing they describe. Since ordinals are used in a sentence as adjectives, they must use the same gender form as the thing they describe. You do this by changing the o at the end of the ordinal to an a. For example, if you were referring to "the second house" on a street, you would write "la segunda casa."

Maintain gender agreement with abbreviations. In English, you've probably seen ordinals abbreviated as "1st" or "2nd." Ordinals can be abbreviated in Spanish too. For example, "1st" in Spanish would be written 1ª if the first thing is a feminine noun, and 1º to describe a masculine noun.

Create multiples similar to English. Multiples are words such as "double" or "triple" that indicate a multiplication of a number. These words are vary similar to the words in English – for example, "double" in Spanish is "doble" – so they should be fairly easy to learn and remember if English is your first language. All but the first seven multiples are created by adding the suffix -plo to the root of the cardinal number word. Be careful of accent marks, which indicate which syllable should be stressed. The first seven ordinals also have forms that end with the -plo suffix (such as "duplo" and "triplo"), but they are seldom used by Spanish speakers.

Change the word form to create verbs and adverbs. In Spanish as in English, you might want to use multiples as a verb (doubled or tripled) or as an adverb (doubly or triply). To form these words in Spanish, you must change the word form. To create a verb, change the -plo suffix to -plicar. To do this with the first seven multiples, you'll have to use that seldom-used -plo form. For example, "to double" in Spanish would be "duplicar." To create an adverb, you simply use the standard adverbial suffix -mente – similar to adding an -ly to form an adverb in English. For example, "triply" would be "triplemente."

Expressing Fractions and Percentages

Learn the word form for different fractions. While halves and thirds have unique words in Spanish, fractions from fourths to tenths are the same as the ordinals for those numbers. The powers of ten also are ordinals. All other fractional words are formed by adding the suffix -avo to the correct cardinal number. For example, if you wanted to write out "one-eleventh" you would write "onceavo."

Use parte with fractions. When you are using the fraction as an adjective, you might add parte immediately after the fraction, just as in English you would add the word "part." For example, if you wanted to express "I took the third part," you would write "tomé la tercera parte."

Write fractional nouns as one word. In English, fractions typically are written out as hyphenated phrases. However, in Spanish any fraction you write using words is written as one word, no matter how long that word is. For example, if you wanted to write out the fraction 1/59, you would write "cincuenta nueveavo."

Choose the correct gender for fractions. The basic rule is that fractions in Spanish are masculine if you are using them as nouns, and feminine if you are using them as adjectives. Fractional nouns that express powers of ten can be either masculine or feminine. Which you use depends on where you are in the world – in Spain they typically are feminine, while in Latin America they typically are masculine. For example, if you wanted to write "one tenth" in Spanish you might write "décimo" in Guatemala, but in Spain you would probably want to write "décima" to ensure you were understood. Fractional nouns other than the powers of ten are always masculine.

Use por ciento to express a percentage. Percents are expressed in Spanish the same way they are in English. You can either write it out with the words or the % sign. For example, you could write either "7 por ciento" or "7%."