Italian forms plurals by changing the final vowel, not by adding an *s*: *-o* becomes *-i* (libro → libri), *-a* becomes *-e* (casa → case), *-e* becomes *-i* (chiave → chiavi), whatever the gender.
The three basic rules
*Masculine in -o → -i**: libro → libri, amico → amici, ragazzo → ragazzi*.
*Feminine in -a → -e**: casa → case, ragazza → ragazze, pizza → pizze*.
*Nouns in -e → -i**, masculine and feminine alike: chiave → chiavi, studente → studenti, notte → notti*. Gender changes nothing here, which simplifies rather than complicates.
A group of nouns ending in -a takes -i because they're Greek in origin: problema → problemi, tema → temi, programma → programmi. They're masculine, despite the -a.
The h that appears from nowhere
Albergo → alberghi*, amica → amiche, banca → banche. That h isn't a whim: it keeps the hard sound of c and g, which would soften before i and e*.
Without it, amiche would be read with the soft c of cena. The rule is spelling, not grammar: it's written differently because otherwise it would be read differently.
The genuine exception is amico → amici, with a soft c. It has to be memorised along with medico → medici and greco → greci.
The nouns that never change
Words stressed on the final syllable: città, università, caffè, tè. Una città, due città.
Foreign words: un bar, due bar; un film, due film; uno sport, due sport. Italian doesn't add the English s, and writing it is a common error.
Shortened words: una foto, due foto; un cinema, due cinema.
In all these cases the article marks the plural, not the noun — one more reason to learn nouns with their article from day one.
Related questions
Why is it amici and not amichi?
It's a genuine irregularity: most *-co* nouns keep the hard sound with an h (albergo → alberghi), but a small group — amico, medico, greco — shifts to the soft sound.
Is it due bar or due bars?
*Due bar*. Foreign words stay invariable in the Italian plural: never with an *s*, which is an English feature.
Updated 2026-07-29