Numbers in Spanish from cero to un millón: spelling rules and ordinals

Spelling the numbers in Spanish: one word or three

The first fifteen numbers in Spanish are single words with no visible pattern; once, doce, trece, catorce and quince continue Latin undecim, duodecim and their neighbours. From sixteen Spanish builds the numbers the way it says them. Dieciséis is diez y seis run together, and veintiuno is veinte y uno, so the letters ie and i in the middle are what remains of the old conjunction.

The Real Academia Española prescribes one word for every number from sixteen to twenty-nine. The spellings diez y seis or veinte y uno belong to older texts. Four of them carry an accent because, written as one word, they end in a stressed vowel or in -s: dieciséis, veintidós, veintitrés and veintiséis.

From thirty-one onwards the conjunction stays visible: treinta y uno, cuarenta y cinco, noventa y nueve. Since the 2010 Ortografía, one-word forms such as treintaiuno are also accepted, but the separated spelling remains the usual choice in careful writing. Y appears only between tens and units, never after a hundred or a thousand, so 101 is ciento uno and 1,005 is mil cinco. Ciento y uno is therefore a non-standard form.

Uno changes before a noun. It drops its -o before a masculine noun and turns feminine before a feminine one: un libro, una casa. The same applies inside compounds, so the language has veintiún años and veintiuna semanas, and the shortened veintiún takes an accent to keep its stress on the last syllable.

Cien or ciento, and hundreds that agree in gender

One hundred on its own, or directly before a noun or before mil and millones, is cien: cien euros, cien mil, cien millones. As soon as more digits follow it becomes ciento: ciento uno, ciento cincuenta, ciento noventa y nueve.

The hundreds from two hundred to nine hundred are single words, and three of them are irregular. Quinientos is five hundred (not cincocientos), setecientos is seven hundred and novecientos nine hundred. The others are regular: doscientos, trescientos, cuatrocientos, seiscientos, ochocientos.

These hundreds have feminine forms, a detail English speakers rarely expect. Doscientas personas, trescientas páginas, quinientas libras: the hundred agrees with the noun it counts, even when other numbers stand between them, as in doscientas una personas.

Mil, un millón and the Spanish billón

A thousand is mil, without un: mil personas, dos mil, diez mil. Mil does not change in the plural when it counts, so 5,000 is cinco mil. Millón is a noun, which shows in three ways: it takes un (un millón), it has a plural (dos millones), and it needs de before the thing counted, un millón de habitantes. The de disappears as soon as smaller numbers follow, so un millón doscientos mil habitantes has none.

Billón is the trap in this part of the numbers in Spanish. It means a million millions, 10¹², the English trillion. The English billion, a thousand million, is mil millones, or millardo in formal and financial writing. Wiktionary's entry records that billón is now sometimes used in the English sense under the influence of English, a use it marks as nonstandard.

In figures, the Ortografía of 2010 separates groups of three digits with a space, as in 15 258, and lets four-digit numbers stand without one: 2026, 3000. For the decimal sign it accepts both a comma, the long-standing custom in Spain and much of South America, and a point, usual in Mexico and Central America, and it recommends the point.

Where Spanish uses the ordinals and where it does not

Spoken Spanish uses ordinals freely up to décimo and much less above it. Above ten a cardinal usually takes their place after the noun: el siglo veintiuno, the twenty-first century, la planta catorce, the fourteenth floor. Kings and popes follow the same rule, Felipe sexto but Alfonso trece, written Felipe VI and Alfonso XIII.

Dates are a separate case. Every day of the month is a cardinal (el dos de mayo, el treinta de junio), with one exception: the first of the month may be el primero de mayo, the form most of Latin America prefers, or el uno de mayo, more usual in Spain.