Plural Forms of Nouns

• Plural Forms of Nouns

If a noun ends in a vowel, make it plural by adding -s.

libro: libros
    (libro + s)

The definite articles (el, la) also change in the plural form. They become “los” and “las.”

If a noun ends in a consonant, make it plural by adding -es.
la universidad: las universidades
    (universidad + es)
el profesor: los profesores
    (profesor + es)

If a noun ends in -ión, add -es and drop the written accent.
el avión: los aviones
la conversación: las conversaciones


If a noun ends in -z, add -es and change the z to c.
la voz: las voces
la actriz: las actrices

When the plural refers to two or more nouns of different genders, the masculine plural is used.
1 gato + 8 gatas = 9 gatos (not gatas)

These compound nouns are always masculine, and the plural is formed by changing the “el” to “los.”
el abrelatas
los abrelatas

http://studyspanish.com/grammar/lessons/plnoun