When do I add -s versus -es?

Add -s when the singular ends in an unstressed vowel (casa to casas, libro to libros). Add -es when it ends in a consonant (papel to papeles) or in a stressed -í or -ú (rubí to rubíes).

Why does lápiz become lápices?

Spanish does not allow -z before -es, so a final z changes to c before adding -es: lápiz to lápices, luz to luces, pez to peces. The tool applies this z-to-c rule automatically.

What about the accent on autobús?

Autobús carries a written accent because the stress falls on the last syllable. In the plural autobuses the stress moves to the second-to-last syllable naturally, so the written accent is dropped. The tool removes such final-syllable accents when adding -es.

Does it handle words ending in -s already?

Yes. A word ending in an unstressed vowel plus -s, like lunes or crisis, is invariable and stays the same in the plural. A word ending in a stressed vowel plus -s, like país or autobús, takes -es (países, autobuses).

Spanish Plural Helper

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Form the Spanish plural correctly

Spanish pluralisation is mostly regular but has several real rules that catch learners: when to add -s versus -es, the z → ces change (lápiz → lápices), accent shifts (autobús → autobuses), and invariable words ending in unstressed -s (el lunes → los lunes). This tool applies the actual rules of the Real Academia Española to give you the right plural and tells you which rule fired.

How it works

The tool inspects the last letters and the stress of the singular noun:

ends in unstressed vowel        -> add -s        (casa -> casas)
ends in stressed -á -é -ó       -> add -s        (café -> cafés)
ends in stressed -í -ú          -> add -es       (rubí -> rubíes)
ends in -z                      -> z becomes c, add -es (luz -> luces)
ends in other consonant         -> add -es       (papel -> papeles)
unstressed vowel + s            -> invariable     (lunes -> lunes)
stressed vowel + s              -> drop accent, add -es (autobús -> autobuses)

For words ending in a consonant or stressed vowel + s, it also removes a written accent on the final syllable when adding -es, because the added syllable shifts the natural stress.

Tips and example

autobús returns autobuses (accent dropped), lápiz returns lápices (z→c), papel returns papeles, and lunes stays lunes. The tool covers the regular and common semi-regular patterns; it does not know individual exceptions or loanwords with debated plurals (el club → los clubs/clubes), so double-check rare borrowings. It also assumes the input is a noun or adjective — plural rules for those two classes are the same in Spanish.