Numbers in Italian from zero to a miliardo: IPA, ordinals and rules

How Italian numbers are built

From twenty on, Italian puts the ten first and the unit straight after it, with no and and no space: ventidue (22), trentacinque (35), novantanove (99). Two units start with a vowel, uno and otto, and before them the ten drops its final vowel: ventuno and ventotto, trentuno and trentotto, ottantuno, novantotto. The CLDR spelling rules for Italian encode exactly this.

Tre at the end of a compound takes an accent: ventitré, trentatré, centotré. Alone it is written without one, because Italian marks a stressed final vowel only on words of more than one syllable. Treccani's dictionary shows both sides: the headword is tre, with tré given only as the pronunciation. English Wikipedia's article on Italian orthography explains that the acute é marks a closed e, which is the vowel of tre.

The teens are irregular in the middle. Undici to sedici put the unit first and end in -dici (from dieci): undici, dodici, tredici, quattordici, quindici, sedici. From seventeen the order switches: diciassette, diciotto, diciannove, ten-and-seven, ten-and-eight, ten-and-nine.

Hundreds and thousands join on in the same way, and the whole number is one word up to the millions: centoventitré (123), millenovecentonovantanove (1999), duemilaventisei (2026). Cento drops its o before ottanta in the CLDR spelling, so 180 is centottanta and 188 centottantotto.

Mille, mila and milione

A thousand is mille, but two thousand is duemila. Mila is the plural of mille, used whenever another number stands in front of it, and Wiktionary notes that it is normally joined to that number: tremila, diecimila, centomila. Mille itself, Treccani notes, is invariable. Before mila the CLDR rules shorten uno to un, so 21,000 is ventunmila.

Neither cento nor mille takes uno in front: a hundred euros is cento euro, a thousand people mille persone. Milione and miliardo are different. They are nouns, take un in the singular and a plural ending, and join the noun they count with di: un milione di abitanti, due milioni di euro. Treccani's examples include un milione di sterline and la città ha superato i quattro milioni di abitanti.

Un miliardo is a thousand millions, the English billion. Multiples are usually written as separate words, due miliardi, according to Wiktionary's usage note, and so are the parts after them: due milioni trecentomila.

Uno, un, una: the number one in Italian

Uno behaves like the indefinite article. Before a masculine noun it is un or uno following the article rules (un libro, uno studente), before a feminine noun una or un' (una casa, un'ora). The CLDR rules for feminine numbers give una for 1.

Due, tre and the rest never change for gender. Tre also causes a small sound change: Treccani marks it with raddoppiamento sintattico, which means the first consonant of the next word is doubled in standard pronunciation, so tre metri sounds like tremmetri.

Decimal comma and thousands point in Italian

Italian writes a comma for the decimal point and reads it as virgola: 3,5 is tre virgola cinque. Thousands are grouped with a point, so CLDR formats one million two hundred thirty-four thousand as 1.234.567,89 for Italy. Swiss Italian follows the Swiss habit, and CLDR prints 1'234'567.89 for Italian in Switzerland, apostrophe and decimal point included.

Treccani writes un milione in figures as 1.000.000. Years are read as one number, not in pairs: 1999 is millenovecentonovantanove and 2026 duemilaventisei, the forms the CLDR year rules produce.

A number used as a noun is masculine: il tre, un sette. Treccani's entry for tre lists the everyday cases, from a school mark (ha preso un tre in matematica) and a playing card (il tre di bastoni) to the day of the month (la partenza è stata rimandata al tre).