Why does 21 become ventuno and not ventiuno?

Italian tens drop their final vowel before the words uno and otto. So venti plus uno becomes ventuno and venti plus otto becomes ventotto. The same rule gives trentuno, quarantuno, and ottantotto.

When does tre get an accent?

The digit three is written tré with an accent when it is the final element of a longer number, as in ventitré, centotré, and duemilatré. On its own it stays tre without an accent.

How are thousands written?

One thousand is mille. Higher thousands use the suffix -mila joined directly to the count: duemila for 2000, ventunomila for 21000. The thousands part is written as one word with the rest of the number.

How big a number can it handle?

It converts integers up to nearly one trillion, in the hundreds of billions range. Millions use milione and milioni, and billions use miliardo and miliardi, written as separate words.

Does cento change before uno and otto?

Yes. Like the tens, cento drops its final o before uno and otto, giving centuno for 101 and centotto for 108. The same elision produces centottanta for 180.

Italian Number to Words

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Spelling Italian numbers correctly is not a matter of stitching words together, because Italian applies vowel elision and accents that change the spelling. This converter handles those rules so the output matches how Italians actually write numbers in full.

How it works

The number is broken into three-digit groups and named with the scale words mila, milioni, and miliardi. Within each group three rules apply:

elision: venti + uno  → ventuno      (drop the tens vowel before uno/otto)
         venti + otto → ventotto
         cento + uno  → centuno       (cento drops its o before uno/otto)
accent:  ...tre at the end of a compound → ...tré  (ventitré, centotré)
mille:   1000 → mille,  2000 → duemila  (suffix -mila, joined directly)

Numbers below twenty are irregular and stored directly (dieci, undici, dodici…). Everything else is built from the tens, the hundreds prefix cento, and the scale words.

Example and tips

The number 1,234,567 becomes un milione duecentotrentaquattromilacinquecentosessantasette — a single run for the part under a million, with un milione separated by a space. For cheques and contracts, the spelled-out form is the legally controlling figure, so the elision matters: write ventotto euro, never ventiotto. The tool accepts grouping dots and spaces in the input and ignores them.